Output Transformer Notes, March 2011.
Updated 2017.
In this page below I have updated some useful notes of 2008.....
Sale conditions for transformers
Speakers, amplifiers and the output transformer
Description of output transformers for sale
Output Transformer Design Parameters

I have provided a comparison of the frequency performance of my own designs and most of
the listed OPTs for sale. See output-trans-freq-analysis-dec-08.html
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Although I have hundreds of power and output transformers and chokes in my stocks, most are widely
different to each other, and the chance that something I have might suit a given project some DIY person
says he wants is remote. And after supplying about 25 items from my large stock of PTs and OPTs,
maybe only 2 customers output about 9 have managed to produce a working power amp, which shows
genuine interest in DIY is at an all time low.

So I will NOT spend a pile of time sorting out what you want
unless you can convince me you are serious about building something.


You need to tell me about your project, and give all details of schematic of the amp and PSU.
Please try to send me a schematic which is well drawn and less than 200kB in file size, .pdf or .gif, .jpg,
Or send me a link to a URL.
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Sale conditions for transformers.
There are no prices for OPTs and you must make an offer which is reasonable to me.
There are prices for PTs.
Freight and packaging to outside Australia may make the total cost too high.
Prices are in Australian dollars excluding freight and packaging.
Payments for transformers can be via direct deposit into my bank account or money order or cheque or cash
and always after email negotiation with Patrick Turner :-

I mostly have pairs of matched Output Transformers and they must be purchased as pairs for dual monoblocs
or a stereo amp.
There are a number of transformers with only one in stock which may suit someone wanting to make only one
amplifier channel.

Mounting brackets, terminals, wire leads, altered air gaps, or any other work will not be included.

All information will be included.
For OPTs, there are usually multiple connections available on the primary winding to suit local cathode feedback,
or various % of screen taps for UL use.

Fuses.
To prevent damage from excessive current, users must connect suitable fuses between each output tube cathode and 0V.
Fuses should be slow blow types with current rating of 3 times the idle current, based on idle current = 0.67 x rated max
Pda / Ea. For 6550 Idle current could be 0.67 x 42W / 470Vdc = 60mAdc.
3 times this idle current = 180mA, so use a fuse = 200mA. Never ever use one fuse to protect more than one tube.
Active protection.
A better way to prevent transformer damage is to fit an active protection board which turns off amp automatically.
Please read examples of active protection at my pages giving full details of power amps I made and sold.
To easily calculate current ability of any wire size based on 2 Amps per square millimeter, maximum average current
allowed in wire = diameter squared x 1.6 where the diameter is the bare copper dia and measured in millimetres.

EXAMPLE :- 0.4mm dia wire has a current ability = 0.4 x 0.4 x 1.6 =  0.256Amps, or 256mA. See my pages deeper
analysis of transformer design parameters. If you had a normal idling current of 60mAdc in a 6550 connected to a
winding of 150r wire resistance, the heat generated is 0.54W. Pd wire = Amps squared x R in ohms.
If the current increases due to bias failure to 600mA, the heat generated increases to 54W and the winding would
soon overheat and damage insulation, and the transformer is ruined beyond repair. If there was a 250mA the
maximum amount of heat in the winding would be 9.4W and the OPT winding would survive.
All PT or OPT with C-cores will be supplied tightly clamped as they appear in images but without support
frames, yokes, or U bolts to allow bolting to a chassis. For SE OPTs, the existing air gap must be assumed to
be incorrect and clamping bands must be removed, C-cores carefully prized apart, and the correct air gap material
inserted according to my pages on SE OPT design.
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Speakers, amplifiers and the output transformer.
Tube amps you may build may produce much less maximum power than most solid state amps and many other
commercially available tube amps. Lower amp power may be acceptable when the tube amp is well matched to
the impedance and sensitivity of speakers. You need to have an overall plan for your sound system , know what
you want in engineering terms, why you want it, and realize you have to spend some real money and a lot of time
 to make a tube amp. You should know the technical specs for your speakers you have now or of those you wish
to buy.
Few people know about resistance, impedance, sensitivity, voltage, current, reactance, LCR theory, phase shift,
Ohm's Law, or anything technical. If you don't know much about technical issues, I will try to give you an OPT
which handles the power needed to create 105 dB SPL from both channels with speaker rated for 1.0W giving
87dB/W/M.
The table below gives my recommendations for amplifier power to satisfy 99% of listeners. Most men enjoy maximum
average levels of 88 dB SPL from both speakers of a stereo system. Most women like lower levels up to 84dB SPL.

Everyone I know with speakers rated for 87dB/W/M is satisfied with 32W per channel where the amp clips with
a speaker of say 0.7 x nominal speaker Z, so if your speaker is nominally "8 ohms", ( 8r0 ) then an amp must make
at least 32W with 5r6. A suitable amp would therefore have a pair of 6550 or KT88 in push pull, like that shown at
Integrated 5050

Table 1 for speaker sensitivity vs amp power and tubes.

Speaker sensitivity, SPL at 1.0W and at 1Metre, dB.	Amp power max for one channel giving 102dB SPL. ( 105dB SPL, both channels used )	Push-Pull Tube type recommended	Single Ended Tube type recommended, Multigrids used as tetrodes/pentodes.
87dB	32W	2 x 6550, KT88, KT90. 2 x EL34, 6L6, KT66, 807. 4 x EL84, 6V6.	1 x 13E1, 4 x EL34, 6L6, KT66, 807, 300B  parallel 3 x 6550, KT88, KT90 parallel.
90dB	16W	2 x 6550, KT88, KT90, 300B. 2 x EL34, 6L6, KT66, 2 x EL84, 6V6 4 x 2A3	1 x 13E1, 1 x 845, 211. 2 x EL34, 6L6, KT66, 807, 300B  parallel 2 x 6550, KT88, KT90 parallel. 4 x EL84, 6V6 parallel.
93dB	8W	2 x 300B, 2A3. 2 x EL34, 6L6, KT66, 2 x EL84, 6V6, 6BM8, 6GW8	1 x 845, 211, 300B. 2 x 2A3  parallel 1 x 6550, KT88, KT90, EL34, KT66, 6L6, 807. 3 x EL84, 6V6 parallel
96dB	4W	2 x 2A3, 45. 2 x EL84, 6V6, 6BM8, 6GW8	1 x 2A3, 6550, KT88, KT90, EL34, KT66, 6L6, 807, EL84, 6V6.
99dB	2W	2 x 2A3, 45. 2 x EL84, 6V6, 6BM8, 6GW8	1 x 2A3, 45. 1 x EL34, KT66, 6L6, 807, EL84, 6V6, 6BM8, 6GW8.
102dB	1W	2 x 2A3, 45. 2 x EL84, 6V6, 6BM8, 6GW8	1 x 45. 1 x EL84, 6V6, 6BM8, 6GW8.

Loudspeakers have  varying impedances at different frequencies bands between say 5r0 and 60r
for what may be a nominal "8 ohm speaker". For something nominally 4 ohms, it is common to find Z dips to 2r8.
The frequency band where low impedance exists is often right between between bass and midrange where most
audio energy is located, ie, between 100Hz and 500Hz where a good quality speaker has 3 drivers, bass, midrange
and treble and where crossover frequencies are at say 250Hz and 3.2kHz.

The manufacturers usually give the SPL generated at 1kHz at 1W at 1M distance and for nominal impedance.
If 1W is needed for 8r0, it means 2.83Vrms x 0.354Arms is needed at the speaker. But where the impedance
dips to a lower value than nominal, the same Vac is needed for the same SPL but more current flows with
lower Z and the power is needed is more than stated, ie, sensitivity is lower for any band of frequencies where
Z is less than the nominal Z.
Many bass, midrange and tweeter drivers have voice coil wire resistance of 8r0, but typical mid band impedance Z
= 6r6, with Z rising each side of the band. They are often labelled 8r0, but are often really 6r0 or 5r0 speakers and
all amplifiers should have ability for highest possible output power for less than the nominal speaker load value.

I once built a few pairs of 3 way full range 'Supreme' speakers where the 3 drivers had mid band Z below dc resistance,
and the average Z for the whole system was 4r5.
The general calculations for crossovers are at loudspeakers-crossover-filters.html
This page explains how good speaker design involves using drivers with individual high nominal Z to make the overall
average Z about 2/3 of the nominal, with minimum Z dip slightly lower.

Manufacturers try routinely to obscure the technical specifications of their products because they know most buyers
have zero technical education and sales are reduced by people chatting to their uneducated friends about impedance,
even though they have little idea of what impedance is.
But there should NOT be large amounts of higher THD and IMD caused by impedance between say 150Hz and 1kHz
being much lower than the nominal or average impedance.
Hence it is always important that for PP amps, the highest maximum AB1 Po is for 3r0 where the amp load is supposed to
be 8r0 as shown on amp output labels, 2r2 for labelled 5r5, and 1r5 for labelled 4r0.

Many amp makers construct their amps to produce highest possible Po with 8r0 connected to labelled 8r0 terminal so
connection of a 6r0 speaker with Z dips to 3r0 cannot possibly produce the full Po. Where there is a labelled terminal
or strapping pattern on OPT, it should be used for ALL speakers and if sound is OKm then always use this 4r0 outlet.

Tube amps need to cope with modern low Z and low sensitivity speakers. Many amps have terminals for
either 4r0 or 8r0 and some have 16r0. always using the 4r0 outlet is always technically OK for amps and speakers,
and is safest against risk of amp overheating.
NEVER EVER use a 4r0 speaker at terminal labelled 16r0.

For where only one load match is possible with just two output terminals, say Com + 8r0, do not use 4r0 speakers.

In my PP 5050 stereo amp the maximum Po possible is about 60W class AB1 with a low amount of initial class A.
But with 8r0 load there is 35WAB1 max, but with a high amount of initial class A1. So my 5050 will cope with
a low load but many other amps would not because amp is designed for max Po 60W for 8r0, and use of 3r0
load would damage the tubes.

For SE amps, max Po should be possible for slightly less than the nominal load so my figures for OP1 to OP16
show sec load = 5r5 which allows for dips of Z below 8r0. 4r0 speakers must not be used.
I hope that all helps people choose from what is available.

For more info on choosing load matches, see my pages on load matching to SE and PP tetrodes, pentodes and triodes.
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Description of output transformers for sale.
Most transformers have have grain oriented silicon steel double C-cores, made by AEM in Sth Australia before
about 1999 when AEM ceased manufacturing C-cores. Some have even better C-cores made in Sth Africa.
The maximum permeability of the C-cores, µ-max, with no air gap is above 4,500 and entirely adequate.
Music sounds excellent with these cores. These GOSS cores give excellent technical performance with low
iron related distortion artefacts which are much lower than harmonic artefacts produced in the vacuum tubes
even at high levels and down to 50Hz or lower where transformers produce most of their distortion. They are
most suitable for tube amp DIY projects or perhaps repair or upgrade replacements. Makers such as McIntosh
used C-cored transformers.
The low loss low distortion C-cores in OPTs offer lower iron caused distortion than ordinary non grain oriented
E&I laminations. Core heating is negligible in all OPTs because the magnetic flux density, Bac, is much lower than
for power transformers. But C-cores offer negligible benefit in guitar amps where amplifier THD and IMD is much
desired to add to the frequencies produced in strings. 
The transformers all have carefully layer wound wire with at least 0.15mm polyester insulation between every layer
of wire. Leakage inductance is extremely low due the extensive amount of primary and secondary interleaving,
resulting in very wide potential bandwidth if the driving source resistance is low enough. Many OPTs have what
I think is an excessive amount of interleaving, with an equal high number of both P and S sections with one layer
of wire in each. So winding losses are usually very low.

The bobbins have a 3mm base wall thickness with ends of wire layers all kept back 3mm from the edge of the
insulation to maximize crepage distance. This was the most common old fashioned and best way to wind a bobbin
where the wire insulation was not polyester-imide for grade 2, and Vac and Vdc was over 1,000V.
With 0.22Nomex insulation used between each P and S layer, it is fairly easy to keep layers flat as they are
wound because the insulation has enough rigidity to not bend down at ends of layers as occurs where insulation
is say 0.05mm between say 4 consecutive primary layers. The practice of keeping wire turns 3mm away from
edges of insulation layers is not needed for tube amp OPTs with grade 2 wire and Vdc less than 1,000V.

Some listed transformers may be used either Push Pull or Single Ended projects. A transformer meant originally
for PP with no air gap may be changed to having an air gap by removing C-core clamping bands, removing C-cores,
inserting gap material to suit the intended use, and re-assembling and re-clamping cores, and then soaking
in epoxy casting resin to prevent any future core movement. M5 u-bolts may be used with a 4mm aluminium plate
to allow clamp C-cores and allow bolting to a chassis. On most OPTs, there are accessible connections between
primary sections to allow selection of CFB windings or UL taps.
Where an OPT originally meant for PP operation has been listed as suitable for possible SE operation, the
maximum SE primary winding dc idle current has not been allowed to to exceed 2 Amps dc per square millimetre
of copper wire section area.
So if the wire size is 0.3mm Cu dia, Cu section area = 0.071sq.mm, and Idc max = 141mAdc. The OPT may
have ZR say 2k8 : 4r0 or 16r0, and with Iadc = 0.141Adc, Po max = 28W. This needs 280Vrms, so Ea may have
to be about 450Vdc. Use of 16r0 winding arrangement with 4r0 gives RLa = 700r, and for 28W, Va = 141Vrms, so
Ea = 250Vdc approx and Iadc would be 280mA which much exceeds the safe level of 141mA.

For all PP OPTs, I have aimed to have nominal power with high initial class A with load = 5r5 so that all RL above
3r0 will be OK.

For all SE amps, max possible Po is with 5r5, and use of speakers above 4r0 only is recommended.
Most of these OPT have only two possibly useful ways of connecting the secondaries to vary the load matching
which gives 4r0 for all secs in parallel and 16r0 with 1/2 the secs in series with other 1/2. There are no other
possible useful loads between 4r0 and 16r0, so I chose 5r5 as design center using 4r0 original intended load.

The general the total winding losses in C-cored transformers are usually low because most have a large winding
window area ratio to central iron core area compared to wasteless E&I laminations so wire diameter is generous.
The designer has selected saturation frequency to be not lower than 32Hz at maximum Vac for maximum Po at
1kHz.
This means the primary turns are about 2/3 those in a same sized transformer with Fsat = 20Hz at the same Vac.
Thus primary wire dia is large for PP operation when primary and secondary winding losses will be lowest.
SE use always results in higher winding losses. The interleaving between primaries and secondaries in most OPTs for
sale is excessive. Most have alternative single layers of primary and secondary from the bottom of the bobbin to the top.
Thus these C-cored output transformers have extraordinarily low leakage inductance and far below what is regarded
as low by the experts of 1953 who wrote the Radiotron Designer's Handbook.
However, there is much higher shunt capacitance than what is regarded as low by the same experts, but for most
applications where the Vac source R driving the OPT is low, the high shunt C may not cause excessive open loop gain
reduction or phase shift beyond 90 degrees and below say 30kHz. I used a number of these OPT with high shunt C
and low LL and found HF instability was not a problem when NFB is used carefully with HF Zobel gain shelving
networks.
The output reactance of an amplifier with these transformers is basically capacitive because it is capacitance which
causes the frequency attenuation above 20kHz rather than the presence of leakage inductance.
I have prepared a page for deeper design comparison at output-trans-freq-analysis-dec-08.html
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Output Transformer Design Parameters.
For OP1 to OP16, there is the following listed information and allows anyone to calculate all other transformer
design parameters :-

Weight in Kilograms; 1Kg = 2.25 pounds.
Overall size as shown, Length horizontally across the two C-cores, Width across the external windings,
Height of C-cores including clamping straps. These dimensions are taken with the transformers oriented as
they appear in the pictures. Dimensions all in millimetres, 25.4mm = 1.0 inches.
Anode Load to Speaker Load ratios for Push-Pull and Single Ended use.
Clipping Power, Class AB1 PP or SE class A1.
The amount of class A1 within PP amps is a variable depending on the Idc at the OPT CT.
Ea is the supply dc voltage applied between cathodes and transformer input excluding cathode biasing if used.
Eg2 is the screen voltage used with nominated tubes if beam tetrode or pentode is employed;
Ea = Eg2 for triode and ultralinear.
Core dimensions are usually given as T x S x L x H for E&I laminations and C-cores. T = Tongue = width of
the central leg of the E+I iron penetrating the winding, or twice the build up of wound strips in C-cores.
S = Stack = height of the E&I lamination stack penetrating the winding, or the width of the wound strips in C-cores.
L = Length of winding window for both E&I lams and C-cores, H = Height of winding window for both E&I lams and
C-cores. Dimensions are all in millimetres.
Np is the number of Primary turns. The turns per layer and wire Cu diameter is given where possible.
Ia maximum dc current is at 2 Amps per sq.mm.
Ns is the number of Secondary turns. The turns per layer and wire Cu diameter is given where possible.
The Interleaving pattern is the arrangement of Primary and Secondary winding sections.
Ips is the insulation between primary and secondary windings.
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Below are calculated results for OP1,
worked out to be optimal for OP1 only but other options could be calculated depending on tube RL,
B+, and idle currents.

Keen prospective buyers will do the necessary loadline analysis for the use of the transformers.

At other pages at my website the methods for designing output transformers are outlined.
The winding losses and bandwidth performance can be calculated from the listed information supplied
with each transformer.

Please do not expect me to carry out YOUR job of working out what you want in complete detail.
But I usually do offer advice and schematic after purchase. 

If you design any output transformer, you should be able to copy the tables below and fill in the right hand
column with relevant figures for the PP or SE design you propose. When you have all 54 listed items filled in,
you should be able to calculate the shunt capacitance, the leakage inductance, and the winding resistance
losses to confirm that your design will give low distortion, enough power, and wide bandwidth.

The 2 tables have the same 54 items listed and some are Not Applicable depending on whether you are
working something out for either PP or SE. Feel free to copy and paste a table to a folder where you can
delete all the right hand numbers, then print a copy of the blank template you will have so that your
calculations on paper in your exercise book may be written down, then copied for a PC folder storage.
I doubt you will come up with better suggestions than I have included for the 16 varieties of OPT
listed in high detail.

Table 1 for OP1 Push Pull use.

1	Output transformer number,	OP1
2	Push Pull or Single Ended ?	PP
3	Weight in Kg	7.4
4	Overall size, length x width x height, mm	176 x 132 x 138
5	Turn ratio, TR, Pri to Sec	23.7 : 1
6	Impedance ratio, Pri to Sec, ohms	562 : 1
7	Primary load x secondary nominal centre load value, ohms.	2,845 x 5.0
8	Primary turns, NP, and wire size, Cu dia, mm	1,496 x 0.45
9	Primary layers x turns per layer	11 at 136t
10	Primary section number, all in series,	11
11	Secondary turns, NS	63
12	Secondary layers x turns per layer x wire size, Cu dia, mm	12 x 63 x 1.0
13	Number of parallel Secondary sections x Secondary turns per section	12 x 63
14	Grain oriented steel core with max µ > 4,500, description	double C-cores
15	Afe, Tongue x Stack, or total strip build up x strip width, T x S, mm x mm	52 x 52
16	Window size, L x H, mm x mm	76 x 28
17	Iron path Magnetic Length, ML, mm	296
18	Insulation, Nomex or other, P to S, mm	0.22
19	Average turn length, TL, mm	300
20	Primary winding resistance, RwP, ohms	50
21	Secondary winding resistance, PwS, ohms	0.036
22	Total winding resistance RwP + RwS at primary, ohms	70
23	Total winding losses, %	2.5
24	Maximum allowable current density in any winding at idle, Amps dc per sq.mm	2
25	Maximum continuous allowable dc or ac current, primary wire, Amps	0.48
26	Maximum design value for dc current, primary wire, for SE operation, Amps	NA
27	Load values for tests, primary anode load x secondary load, ohms.	2,845 x 5.0
28	Nominal Anode Source resistance ( between highest and lowest Ra possible ) for tests, ohms	2,845
29	Maximum primary inductance, PP operation, Lpmax, no air gap, µ > 4,500, Henrys, H	128
30	Minimum Primary inductance, PP operation, Lpmin, approximate, no air gap, µ = 1,000 at low Vo, Henrys, H	28.4
31	Effective permeability, µe, with air gap for SE operation, Bdc = 0.75Tesla	NA
32	Air gap calculated for reducing maximum iron µ to above wanted µe, mm, ( confirmed by experiment in amp )	NA
33	Non magnetic material thickness used to gap cores on both breaks in magnetic loops, mm	NA
34	Primary inductance, Lp, for SE operation, for µe, Henrys, H	NA
35	Leakage Inductance, at primary input, LL, mH	0.24
36	Shunt capacitance, at each anode primary input/s, pF	3,000
37	Maximum audio power at anodes for THD < 2%, at 1kHz, at rated RL loaded, Watts	135.0
38	Maximum anode signal voltage across primary at THD < 2%, Vrms	620
39	Maximum class AB1 power, PP operation, at rated RL, Watts	135
40	Maximum class A1 power at rated RL, Watts	30
41	Frequency of core saturation at max audio power signal across primary at Bac + Bdc = 1.5 Tesla, Hz	22.3
42	Low frequency cut off at 0.1 x max Vo, source resistance = 1/2 anode RL, Hz	8
43	High frequency cut off with Secondary loaded. Primary source resistance = primary RL, kHz	75
44	Tubes usable, type numbers	6 x KT88
45	Tube configuration, Ultralinear, UL, Cathode Feedback, CFB, Pentode, P, Beam Tetrode BT, Triode, T.	UL, CFB
46	Maximum Idle dc anode and screen dissipation power setting for each tube, Pda, Watts	25
47	Maximum total tube idle dissipation power Pda, Watts	150
48	Anode to cathode dc supply voltage ( excluding possible cathode biasing voltage ), Ea, Vdc	500
49	Total Idle condition anode and screen supply dc current for all output tubes, Idc, mAdc	300
50	Anode plus screen Idc per tube, mAdc	50
51	Actual anode plus screen dissipation in each output tube ,Watts	25
52	Maximum Idc needed for maximum output power for stated load, approximate, mAdc	500
53	PP tolerated loads with the tubes above, Primary load : Secondary load, ohms.	1,686 : 3.0 2,248 : 4.0 2,800 : 5.0 3,372 : 6.0 4,496 : 8.0
54	SE tolerated loads with the tubes above, Primary load : Secondary load, ohms	NA

Table 2 for OP1 Single Ended use.

1	Output transformer number,	OP1
2	Push Pull or Single Ended ?	SE
3	Weight in Kg	7.4
4	Overall size, length x width x height, mm	176 x 132 x 138
5	Turn ratio, TR, Pri to Sec	11.85 : 1
6	Impedance ratio, Pri to Sec, ohms	140.5 : 1
7	Primary load x secondary nominal centre load value, ohms.	711 x 5.0
8	Primary turns, NP, and wire size, Cu dia, mm	1,496 x 0.45
9	Primary layers x turns per layer	11 at 136t
10	Primary section number, all in series,	11
11	Secondary turns, NS	126
12	Secondary layers x turns per layer x wire size, Cu dia, mm	12 x 63 x 1.0
13	Number of parallel Secondary sections x Secondary turns per section	6 x 126
14	Grain oriented steel core with max µ > 4,500, description	double C-cores
15	Afe, Tongue x Stack, or total strip build up x strip width, T x S, mm x mm	52 x 52
16	Window size, L x H, mm x mm	76 x 28
17	Iron path Magnetic Length, ML, mm	296
18	Insulation, Nomex or other, P to S, mm	0.22
19	Average turn length, TL, mm	300
20	Primary winding resistance, RwP, ohms	50
21	Secondary winding resistance for NS, RwS, ohms	0.144
22	Total winding resistance RwP + RwS appearing at primary input, ohms	70
23	Total winding losses, %	9.0
24	Maximum allowable current density in any winding at idle, Amps dc per sq.mm	2
25	Maximum continuous allowable dc or ac current, primary wire, at 2Amps/sq.mm Cu,	0.324
26	Maximum design value for dc current, primary wire, for SE operation, Amps	0.324
27	Load values for tests, primary anode load x secondary load, ohms.	711 x 5.0
28	Nominal Anode Source resistance ( between highest and lowest Ra possible ) for tests, ohms	711
29	Maximum primary inductance, PP operation, Lpmax, no air gap, µ > 4,500, Henrys, H	NA
30	Minimum Primary inductance, PP operation, Lpmin, approximate, no air gap, µ = 1,000 at low Vo, Henrys, H	NA
31	Effective permeability, µe, with air gap for SE operation, Bdc = 0.75Tesla	278
32	Air gap calculated for reducing maximum iron µ to above wanted µe, mm, ( confirm by experiment in amp! )	1.0
33	Non magnetic material thickness used to gap cores on both breaks in magnetic loops, mm	0.5
34	Primary inductance, Lp, for SE operation, for µe, Henrys, H	7.9
35	Leakage Inductance, at primary input, LL, mH	0.3
36	Shunt capacitance, at each primary input/s, pF	5,000
37	Maximum audio power at anodes for THD < 2%, at 1kHz, at anode rated RL loaded, Watts	36.0
38	Maximum anode signal voltage across primary at THD < 2%,	160
39	Maximum class AB1 power, PP operation, at rated RL, Watts	NA
40	Maximum class A1 power at rated RL, Watts	36
41	Frequency of core saturation at max audio power signal across primary at Bac + Bdc = 1.5 Tesla, Hz	14.4
42	Low frequency cut off at 0.1 x max Vo, source resistance = 1/2 anode RL, Hz	7
43	High frequency cut off with Secondary loaded. Primary source resistance = primary RL, kHz	75
44	Tubes usable, type numbers	4 x KT88,6550
45	Tube configuration, Ultralinear, UL, Cathode Feedback, CFB, Pentode, P, Beam Tetrode BT, Triode, T.	SEUL, SECFB
46	Maximum Idle dc anode and screen dissipation power setting for each tube, Pda, Watts	25
47	Maximum total tube idle dissipation power Pda, Watts	150
48	Anode to cathode dc supply voltage ( excluding possible cathode biasing voltage ), Ea, Vdc	295
49	Total Idle condition anode and screen supply dc current for all output tubes, Idc, mAdc	350
50	Anode plus screen Idc per tube, mAdc	86
51	Actual anode plus screen dissipation in each output tube ,Watts	27
52	Maximum anode Idc needed for maximum output power for stated load, approximate, mAdc	330
53	PP tolerated loads with the tubes above, Primary load : Secondary load, ohms	NA
54	SE tolerated loads with the tubes above, Primary load : Secondary load, ohms	423 : 3.0 564 : 4.0 711 : 5.0 846 : 6.0 1,128 : 8.0

Good luck!

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