two el34s paired with a 100 Watt OT

[Guitarist]

Apparently my Traynor has, from the factory, a HUGE 100 Watt output transformer. IIRC, to compensate I should half the speaker impedance. Stock, the impedance wire from the OT is an 8Ω. Thus I'm forced to use an 4Ω cab.

If I'm aiming for a Marshall/Friedman FB resistor value of 27KΩ, might you have a recommendation for this FB resistor now?

[alexradium]

You want to double the impedance to match the 2 power tubes, but you need to measure turn ratios anyway before making choices.

[Chuck H]

Apparently my Traynor has, from the factory, a HUGE 100 Watt output transformer. IIRC, to compensate I should half the speaker impedance. Stock, the impedance wire from the OT is an 8Ω. Thus I'm forced to use an 4Ω cab.

If I'm aiming for a Marshall/Friedman FB resistor value of 27KΩ, might you have a recommendation for this FB resistor now?

You want to double the impedance to match the 2 power tubes, but you need to measure turn ratios anyway before making choices.

This^^^^^^^^^^^^^^^^^^^^^^^^^

But I'm curious. Are you saying you believe Traynor (incorrectly or mistakenly) installed a 100W OT into an amp that is a two power tube model? And if so then you believe that the 8 ohm tap Traynor provided is incorrect?

[Jazz P Bass]

The wattage of the transformer has nothing to do with the impedance ratio.

Do what Alexradium suggests and find out what the ratio is.
The Ratio will dictate the tube setup.

[nosaj]

This^^^^^^^^^^^^^^^^^^^^^^^^^

But I'm curious. Are you saying you believe Traynor (incorrectly or mistakenly) installed a 100W OT into an amp that is a two power tube model? And if so then you believe that the 8 ohm tap Traynor provided is incorrect?

Just to chime in the hammand transformer on my 79 traynor is bigger than a similar fender 50 watt. Mine is a 50 watt.
Nosaj

You should cross reference the part number first.

[g1]

If it is all stock, the labelling from the factory will be correct. I'm really not sure why you would be second guessing this. Traynor used large transformers in most of their vintage amps.

[loudthud]

The YBA-1A's prior to 1970 had huge output transformers. Normally they only used the 8 Ohm tap, if you take off the end bell, there is a 16 Ohm tap wire that is cut short.

[mozz]

And the YBA-1A's, well the few i have seen, do not have the output impedance marked on the back of the amp.

[Chuck H]

The YBA-1A's prior to 1970 had huge output transformers. Normally they only used the 8 Ohm tap, if you take off the end bell, there is a 16 Ohm tap wire that is cut short.

Good to know

[g1]

It should also be mentioned, this is more of a 100W amp, and there are others that also get similar power from a pair of EL34.
The impedance of the OT has nothing to do with the power rating. So for this amp, the transformer is sized accordingly.

Thanks for the data Mozz. https://www.aguitarforum.com/threads/nutad.90883/
https://music-electronics-forum.com/...ad.php?t=42311

[Guitarist]

Thank you so much for sharing your experience for which there is no substitute. I did look up previously the parts numbers via Hammond's site and it is listed as a special order (now) 100 Watt OT. Generally I run speaker cabs in parallel so if I approach a 4Ω or even 2Ω load, I trust that'll be fine.
I do also have a PPIVMV that I added

So this'll likely be my forever-amp from here on as it is so easy to work on and on and on...
I am starting to build an inductive-resistive load box for it from coils pulled from a Celestion crossover...if that works out then an effects loop would be moot. But it is tempting to add one, preferable parallel.

[Chuck H]

Um... I think that's the power transformer.

[Guitarist]

Ah ok, there were a few unlabeled pics from an email I sent them months back. Here's the OT then!

[Guitarist]

I found matching numbers at the bottom of Hammond's 1750R spec sheet.
I am considering buying a pair of tubes that might best match this 100 Watt OT but within high plate dissipation limits. I don't mind if they're 6cA7, 6L6 or Shauang KT120s.

What pair of tubes would best match a 2000Ω C.T.? IDK, it seems that when people talk of OT they double this C.T. value. So should I refer to as 4K? The amp's plates are seeing 540V. Would I lower the FB resistor?
I read elsewhere that a 6L6 likes a 6.6kΩ load. 6V6 an 8K Load. "If you go with KT77, EL34's I'd go with 3.5K/4K @ 400V B+"

Running high primary impedances is maybe a Trainwreck thing. Running low primary impedances is a Marshall thing."
Orange also uses 100 OTs in the 50 watter: "Output transformer for: Orange® 120 W Amps, also used in the OR80 amps Fits Orange Matamp OR100 also!" But they just half the Ωs written on the back. So if there was a 16Ω second wire, they'd disconnect that and use the 8Ω.
If I get more 2nd order distortion and less power that's ok with me

BTW, I added Marshall grill cloth over the 70s silvery. Also white chicken head knobs. I had some NOS concentric and switch pots to fill out the panel options and added some Friedman-esque mods and relay switch bettered Plexi and 800.

[Helmholtz]

What pair of tubes would best match a 2000Ω C.T.?

A 2k primary is not suitable with any pair of tubes I know.

IDK, it seems that when people talk of OT they double this C.T. value. So should I refer to as 4K?

No.
You can double primary impedance by doubling load impedance, though.

I read elsewhere that a 6L6 likes a 6.6kΩ load. 6V6 an 8K Load. "If you go with KT77, EL34's I'd go with 3.5K/4K @ 400V B+"

Fender amps typically use 4k to 4.5k with a pair 6L6s. Otherwise correct.


I'm quite sure this 1750R OT is meant for a quartet of power tubes.
More OT discussion here:https://music-electronics-forum.com/...elp#post977921