Traynor YGM-3 (early) - Selmer cab

[Barks]

Yes - 432.

I'll open it up again and re measure as directed.

[martin manning]

No rush on the screen voltage, just curious.

Sounds like it has shaped up quite well! With several things changed, it's hard to say what fixed what, but I think the farting was most likely from failing valves, and if that set is badly miss-matched I wouldn't use them. The other odd noises were most likely cleared up with the addition of screen resistors, IMO. Lower idle current will have some effect on the tone, but the biggest benefit there is prolonging valve life. Don't forget you're also much better off on that score with the lower heater voltage the new PT is providing.

[Barks]

OK - did 3 sets of measurements with different trim settings

Measured Pin7 anode to ground
Measured Pin 3 cathode from non-ground side of 10ohm resistor, to ground
Measured Pin 9 screen resistor to ground

Do I use the screen v reading when calculating?

Measurement One:

V3 Anode - 428v
V3 Cathode -28.5 mvolts
V3 Screen - 427v

V4 Anode - 428
V4 cathode - 26.5 mvolts
V4 Screen - 426v

Measurement Two:

V3 Anode - 430v
V3 Cathode -21.2 mvolts
V3 Screen - 428v

V4 Anode - 430
V4 cathode - 19.6 mvolts
V4 Screen - 429v

Measurement Three:

V3 Anode - 432v
V3 Cathode -19.9 mvolts
V3 Screen - 429v

V4 Anode - 432
V4 cathode - 18.6 mvolts
V4 Screen - 429v


Does this look like correct behavior. The screen resistor seems to be knocking the voltage down a little bit.

[Barks]

Just another curious note.

the amp has been on for about 2 hours now and I did the 3 measurments about 20 minutes ago - so the amp was at operating temp/conditions.

Just rechecked the anode and the voltage has gone up to 434-5 volts.
is this common that it will move around a bit when idling.

[Barks]

haha - it's gone back down to 432!

I've not changed anything. It's been left on in non-standby mode and at idle.

could this be a "dirty mains" issue with swings in voltage from the outlet?

[martin manning]

Yes, those all look reasonable, and the screen being a bit lower than the anode is a good thing. There will be some subtle difference in tone as you vary the idle bias, but in general being in the 60-70% of Pa max is fine. As you can see the currents don't match exactly, and that is just due to the manufacturing tolerance in the valves. No doubt you have seen matched sets offered, and perhaps matched, burned-in sets too. Some amps have a bias trimmer for each side of the OT. Being within a mA or two is fine though.

[martin manning]

Yes mains voltage will vary over the course of a day due to changing demand, and your DC voltages will go up and down accordingly. Its best when recording voltages to also get the mains voltage both before and after taking readings. You can also use a Variac to set a standard reference input voltage (240).

By the way where is your mains running now?

[Barks]

Thanks.

The previous older two were matched TAD valves as well, but the difference was greater.
I suppose I lucked out on these Hotrox matched TADs.

In the UK it's sunny right now so the general populace are not brewing cups of tea!

[martin manning]

Over here warm weather will lower the mains due to high-current air conditioners coming on-line.

[Barks]

The mains are fluctuating between 249 and 253

[martin manning]

So if it was running at the standard 240VAC, your anode voltage would be down around 413.

[Barks]

It seems that the voltage in the UK can vary between 216v and 255!

I never knew that. These are the legal limits.

If I have a voltage of around 250 it means I'm near a substation.
This will account why I get more induced low level hum in some unbalanced gear in my studio at night time.

http://www.soundonsound.com/sos/jul03/a ... oblems.asp

[rp]

Not necessarily dirty power just varying. Not necessarily the power co's fault either, people may have all their ac's on, or 9am all the stores/offices light up, 6pm they all go off, etc. Maybe your neighbor's running a floor sander?

Others can chime in but ~430V plate w/ ~430V screens is extreme. Those small glass bottles don't dissipate a lot of heat. God bless TAD tubes but if they fail after a few days it wouldn't be unexpected - good thing you have those 1/4W "fast-blow fuses" installed. Might want to take a back up amp to the gig.

I would try changing the 470R dropping resistor btwn the first two caps to 1K and change the screen grid ones to 1K also (check bias after) just to give the tubes a fighting chance. And all this time I was worried that my Matchless clone at 345V was going to eat up my small supply of NOS EL84s

If they hold up report back in a month. Blow my mind.

[Barks]

Ok, at the last setting where it was 432 I was averaging @69-70%.

I think I'll leave it there for now and enjoy the amp. I need to be confident it'll hold up at the next gig on Sunday.

The amp could sound different at different venues just because of the outlet voltage - let alone the acoustics.

Thanks everybody - I have learned a lot

[Barks]

If they hold up report back in a month. Blow my mind.

Will do!

Just remember it operated at 456v and 7.5 heater for the last 20 years and never failed.
Tubes just got tonally soft after about 6-9 months constant use.