Do Screen grid resistors need to be 5w Dale rs5's?

[TheElectricMoron]

I don't recall any shared 10watters in the YGK3MIII at all.. Doesn't mean it wasn't like that but the schemo I have doesn't have it either. I do remember replacing a raft of 1watters.

Definitely NBD to me since whatever it was ain't no more.

I built a PrincetonReverb w/ a 2xEL34 output into a Bassman chassis/trannies. Got it in a 1x15". Cathodyne PI rocks. The output is wired like the Traynor and the thing gets cranked allllll the time. Nothing bigger than a 2watt in there even on the rail and it's just fine. Life on the edge?

FWIW

Charlie

[talbany]

but the schemo I have doesn't have it either

Charlie
Not to beat a dead hoarse here but take a look at the bottom of the YGL-3A..Schemo you posted... You can see the note Pete Traynor wrote about setting bias..

"adjust bias supply for 8 volt DC across R57 (470 10w) with no signal applied"

Traynor spec'd the bias on these old amps as a function of idle screen current. That's what you're really measuring when you check the voltage drop across the single screen resistor R57
They call for an 8 v drop. What they're really measuring is the combined screen current at idle (only way to do this is through 1 resistor) . Old Pete Traynor figured that when the combined plate idle current was about right then the total screen current would cause an 8 vdc drop across R57..

Are you sure your not confusing grid resistors w/screen resistors?

Tony.

[Structo]

Interesting enough, the Amperex EL34 documents lists specs for a fixed bias, push pull, that a 1K screen is required for each screen grid to prevent screen overload.

So if a 1960 data sheet is calling for a 1K screen resistor that is good enough for me.

Concerning the Traynor amp, why only V8 and V10 have an additional 47 ohm G2 resistor?
There is the common 470 ohm resistor but then they have the 47 ohm resistors on only two of the four tubes.

This schematic is a little clearer.
http://www.webphix.com/schematic%20heav ... gl3_3a.pdf

[talbany]

Interesting enough, the Amperex EL34 documents lists specs for a fixed bias, push pull, that a 1K screen is required for each screen grid to prevent screen overload.

So if a 1960 data sheet is calling for a 1K screen resistor that is good enough for me.

Concerning the Traynor amp, why only V8 and V10 have an additional 47 ohm G2 resistor?
There is the common 470 ohm resistor but then they have the 47 ohm resistors on only two of the four tubes.

This schematic is a little clearer.
http://www.webphix.com/schematic%20heav ... gl3_3a.pdf

Tom
I don't know why he used 47 ohms there..Perhaps you can find out for us..I know the Hiwatts used a similar type configuration but used 100 ohm- there so you could weed out bad EL34's and then measure and compare Screen-Grid voltages. The 470 is the one drawing the most current..
An example would be... If the voltages you measure are (A)520VDC, (B)518VDC, (C)521VDC, and (D)493VDC, the last EL34 (tube 'D') is 'bad'. It is drawing excessive screen current, and that tube should be tossed A volt or three of difference is nothing to worry about; you are looking for the tube with a considerably lower Screen Grid voltage.
Tony

[Gaz]

Since this thread has transformed into being about Traynors (however still applicable to Dumbles and others), I should mention that I recently measured screen dissipation on a YBA-3 which has a high plate and screen voltage around 530vdc. Amazingly the amp did not over-dissipate its screens, even at max signal! This is with the shared screen resistor, and small individual screen resistor set up.

Was this because of unique screen grid set up? No. Because of the suppressor grid being tied to the raw bias supply. Nope. It turned out it was simply because the screen voltage had 'poor' enough regulation to let screen supply sag far down enough (to about 400vdc, IIRC) to keep the screens from over dissipating.

I really don't how it was possible, because the PT in this amp was huge! I personally don't use the special suppressor grid connection, because I fear a fairly common screen failure would take out the bias supply. I know Merlin for one has argued that the g3 connection is kinda BS anyway.

I never worry about much of this for a Dumble anyway that develops most of its goodness in the pre.

[talbany]

GAZ
Personally I never liked the way the output section in those Traynor's sounded.. Sterile and gritty..Don't know if it's the screen supply set up or the higher voltages!!... Pete did use some nice Hammond Iron though!!
PT on YBA1A MRK II=25lbs
BTW... Never understood how and if he could get 90w out of a pair of 34's in non UL mode..

Tony

[Gaz]

Tony, sterile and gritty is right, which is kinda surprising considering how much sag is happening. I've got the same problems with V4s, another amp with super high B+ and little screen resistance.

[TheElectricMoron]

Like I said, it's been a long time since I was in that amp, but I do remember replacing a handful of bits and pieces. All the screen and grid resistors, preamp plate loads, filters, bypass caps - I mean I went thru it. Sorta a PITA too since Traynor didn't do the layouts in a "logical" kinda Fender way. The YGM amps are the same way.
Anyway what I had when I was done with that was still pretty much Traynor. The big diff was swapping in a couple Celestions and it most certainly did not sound sterile and/or gritty. Every Traynor combo I've worked on has benefited in a big way by a speaker change.
The EL34 amp I built is driving a 15"JBL and it certainly doesn't sound sterile or gritty. I don't think the suppressor grid trick is in any way detrimental to the sound.

JMO of course - - - YMMV

Charlie

[David Root]

Thank you, I was kinda wondering about that.