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

[Joost]

From what i understand the screen grid resistors on a 124 should be Dale rs5s. I can't get them anywhere and mouser is out of stock. So is it ok to use Dale CW5 wire wound 5W resistors? Or should I wait for mouser to get the rs5s in stock?

[ToneMerc]

The originals were 470 ohm 3W Sprague Q lines. Just look for a 470 ohm 5W power resistor.

TM

[Kregg]

I thought that anything (film or oxide) 3W and up was fine.

[Structo]

I would definitely use a flame proof type there.

That would be either metal oxide or wire wound.

Those get real hot due to being over the socket.

Three watt is probably OK but I like to use five watt there.

[Kregg]

Hey Tom, I noticed that you have a picture of my younger brothers childhood knife in the outlet incident! He blew out the fuse in the panel and got knocked on his butt.

[talbany]

Definitely go with the 5w if you plan on using 34's

Tony

[Structo]

Hey Tom, I noticed that you have a picture of my younger brothers childhood knife in the outlet incident! He blew out the fuse in the panel and got knocked on his butt.

Hehehehe,
My little brother liked to chew on extension cords when he was a toddler.

I don't think I ever stuck a knife in an outlet but found other, more creative ways to get shocked.

[David Root]

Tony, with expensive NOS EL34s wouldn't it be safer to use 3W rather than 5W screen resistors?

I just ordered a quad of XF4 Mullards from Gregg Levy and don't want to fry them in a #183 I'm planning. That's an expensive fireworks show!

[TheElectricMoron]

Tony, with expensive NOS EL34s wouldn't it be safer to use 3W rather than 5W screen resistors?

I just ordered a quad of XF4 Mullards from Gregg Levy and don't want to fry them in a #183 I'm planning. That's an expensive fireworks show!

The best way to protect EL34's is to configure them the way Traynor did. check out a YGL3MIII schemo with the bias feed to the supressor grids.

http://www.lynx.bc.ca/~jc/761012_YGL3_3A.gif

a trick that you can't do to 6L6's because of the internal connections in the 6L6 that EL34's don't have as a true pentode.
Try it, it will make you way happy when your EL34's last forever. Mine do.

Charlie

[talbany]

Tony, with expensive NOS EL34s wouldn't it be safer to use 3W rather than 5W screen resistors?

I just ordered a quad of XF4 Mullards from Gregg Levy and don't want to fry them in a #183 I'm planning. That's an expensive fireworks show!

Dave
I suppose there are several ways to look at it..34's by design (all of them) have a wimpy screen supply and when they go,bye bye screen resistor, so in effect 3 watt would go sooner w/ shorter surge time on the power transformer in case your B+ doesn't go..(Which I have seen plenty of Marshalls with burned out screen resistors and a spared B+ fuse) so in that respect a lower wattage screen resistor can be a good thing..On the other hand a single 34's screen supply can dissipate 8 watts when screaming at you causing a 3w to get pretty hot, eventually the 3 watt could flame, shutting down the amp..(I have seen this to where amps have been mod-ed before using 3 watt resistors on a pair of 34's) Generally and in most cases if your screens go doesn't matter 3 watt or 5 watt..instant fireworks and if your lucky a B+ trip..
Moral of the story.. If you run your 34's hard go 5W..


Tony

[David Root]

Thanx EM and Tony. I remember the Traynor mod. I'd like to try both EL34s and 6L6s in the #183. If EL34s win the day I would switch in the Traynor mod.

I would dearly like to put a quad of EL37s in it just to see if they really are the holy grail of 6L6s, but my wife would divorce me and then kill me with a rusty knife if she found out I had spent that kind of money on tubes.....

[67plexi]

The Traynor mod sounds cool.

But in EL-34 amps I use 7 watt wire wound resistors only.

Have had the 5 watt resistors fry, I would rather blow a fuse.

[TheElectricMoron]

Just an added thot - when I rehab'd my YGL3A I replaced all the screen resistors with 2watt flameproof. It had 1watt carbons in there and I'm guessing they were original. Had the original tubes too. No evidence of smoke. I had it a couple years and cranked it all the time. No smoke. I know the guy that has it now. Still no smoke.

You can put giganto resistors on your EL34's but they are a waste of money. Couple pieces of hookup wire will actually do a better job and be just way cheaper too.

I've fixed several Marshalls this same way and they have never had a problem since.

Make your life easy too.

just a thot

Charlie

[talbany]

It had 1watt carbons in there and I'm guessing they were original.

I doubt it... The original has a single 470 ohm 10watt shared screen resistor (I personally like separate ones)..I had a YBA1A MKII that had this setup and that resistor had dissipate enough heat to burn the schematic on the lid..If your using 1 watt carbons on the screen supply of a 34..Better keep a fire extinguisher/or some marshmallows close by..Glad to hear you replaced those..

Tony

[David Root]

I think I will put in the Traynor mod, I looked it up where I first saw it, in TUT 1, p. 6-45 and -49.

You can substitute any 6L6/5881 because pin 1 in not connected to anything in those tubes. It's only the other way around that gets you in trouble, putting an EL34 in a socket wired for 6L6/5881. I will put 1K 3W individual screen resistors in too. That should cover it.