Traynor YGM-3 (early) - Selmer cab

[martin manning]

Barks, YGM-3 schematics show two OT part numbers , A1339 and A1325. Your YGM-3 has A1339, Hammond's A1339 equivalent (1750S) is 5k1 with 8 ohm secondary. If you are up for some tinkering, it would be good to verify the impedance ratio of your A1339 OT. You can do that without taking the chassis out by putting some AC into the speaker jack and measuring voltage there and across pin 7's on the power tube sockets.

[didit]

Just clarifying -- by AC Martin would be suggesting a low voltage into the "speaker" secondary and then measure at pin 7, the primary. Simple method is unplug tubes and jumper 6.3v filament onto secondary and then measure both sides.

Best .. Ian

[martin manning]

On the YGM-3 the standby switch is in the CT of the HT, so I would not recommend using the amp's filament voltage for the AC. If you have a 6V filament transformer or an AC wall wart handy that will do.

[Barks]

Barks, YGM-3 schematics show two OT part numbers , A1339 and A1325. Your YGM-3 has A1339, Hammond's A1339 equivalent (1750S) is 5k1 with 8 ohm secondary. Your pictures seem to show speakers wired in parallel... are they 8-ohms each?

Hi Martin,
Both speakers are 16ohms each.

[martin manning]

Ah (Oops), you could try disconnecting one then.

[Barks]

Run it on 16 ohms with a single?
Sorry, not sure I'm understanding what is trying to be achieved here - to see if it counters the fizz?

The speakers are 16ohms each in parallel so that means 8ohms. The amp has a secondary speaker jack on the back which is labelled 8ohms - so I assumed it was all at the correct impedence rating?

[martin manning]

Sorry, seems like the OT you have has primary impedance at 5k1 with an 8-ohm load (per the spec for Hammond's replacement for your part number). That is low for a pair of EL84, particularly at ~430V on the plates. That would reduce tube life, and may not be the best sound-wise. I don't know if the fizz would be affected or not but it would be interesting to see how the sound changes anyway.

[Barks]

Best I can do ac wise is a 9v wall wart - would that do, probably not!

[Barks]

Just had a little play with it on a single 16ohm. No real difference that I could tell except it's less 3D - probably as the two speakers pushed more air.
It sounds great really - just that slight fizz.

Could you guys hear it on the close mic wav file I uploaded a few posts back?

The original speaker the amp was coupled with would have been a single 8ohm Marsland with a sealed back on the cab -from what info I get from the net.

[didit]

Best I can do ac wise is a 9v wall wart - would that do, probably not!

A 9v AC brick should be fine. Note AC not DC, which bricks for pedals typically are.

And a thank you to Martin for noticing HT potential on standby.

[Barks]

Yes this is 9v ac

[didit]

For various reasons lower VAC works best. Example, your transformer will have about 15V on secondary when working. Testing with more voltage will directly increase voltage on primary and closer to the power limits of the transformer and likely your brick. Doing the math will help understanding. One can also test by putting 9VAC across primary, and working through forward vs backward. It is ratio. Here is reference I believe covers it -- http://www.radioremembered.org/outimp.htm.

But I think you can trust the spec for stock OPT, which 5k1 primary.

Best .. Ian

[martin manning]

You are probably right Ian, but Hammond's replacement might not match the A1339 spec exactly, and 5k1 seems like it would have to result in over dissipation when running 430V on the plates... 6k6 would be much more reasonable.

[didit]

[...] 5k1 seems like it would have to result in over dissipation when running 430V on the plates... 6k6 would be much more reasonable.

Or even 7k5-9k, agreed. Except Hammond made original iron, at least for these el84 amps. Would not expect replacement to be off spec. Propose 400V closer to vintage voltage design target. Still high.

We are off on tangent. How to resolve fizz seems to be a real mystery. Reading yesterday seems some theorize "ringing" OPT iron. Not something I have direct experience with. All remedies seem to be attenuation of higher frequencies. Any thoughts on that?

Best .. Ian

[Barks]

I'll have a look this weekend. Yet to up the grid stoppers as suggested.
One thing that occurs to me is the nature of the speakers.
I've just read that the old Goodmans (Axiom I think in this case) were considered to be more toward hifi than guitar.
I wonder...