6l6 to el34 tube swap?

[sjturbo]

I'm sure many will think this is a question that we all should know the answer to so I may be the only one. I have a MMRD50 with 6l6's and wondered if el34's could be substituted for them with out significant changes? Thanks in advance for your patience!

[Jazz P Bass]

#1 on the list is the power transformer.
-Can it supply the additional heater current that the EL34's require.

It goes without saying that the bias voltage will have to be lowered to accommodate the EL34's.

[Gingertube]

Plus
Check that there is a link between pins 1 and 8 on ALL of the output tube sockets. This to connect the EL34 suppressor grid to the cathode. 6L6 doesn't have a suppressor grid so doesn't need that connection. A lot of amps will have that link in them just so that EL34 or 6L6 can be used. If your amp does not have that link then you will need to add it.

Cheers,
Ian

[Mick Bailey]

Check if pin 1 is used as a tie point for another component such as the grid stopper or screen resistor. If so you will need to move that component end off pin 1 and connect pins 1 to 8 as Ian suggests.

I also like to increase the screen resistors from 470R to 1K for EL34.

[Gingertube]

What Mick says too - important. Even if you leave 6L6 in, changing the screen resistor to 1K 5 Watt Rat Coffin types will extend the life or your tubes.
Cheers,
Ian

[sjturbo]

Ok! Thanks all of you for the great information. Since the MM is stock as I bought it in 82 I think a good work around would be just find a nice 40 or 50 watt el34 that was designed that way.
BTW Gingertube, what is "Rat Coffin" type and do they reduce current/voltage?

[Gingertube]

"Rats Coffin" type is slang for the white ceramic block style power resistor.
Like this one:
https://www.digikey.com.au/product-d...0KW-5-ND/18703
They introduce some screen compression and limit screen power dissipation.
Cheers,
Ian

[nsubulysses]

oh like, that's what you get for squeelin. Mousetrap for a rat

not like an animal rat that nibbles your cookies while you're out.

just some old fashioned mob justice i see

[Leo_Gnardo]

I've seen those called "ant coffin."

[Mick Bailey]

And 'Sugar cubes'

[g1]

and 'sand box'

[Enzo]

Wow, you know, all these names are colorful and fun. In all my years, I never adopted a name for them, I still call them rectangular ceramic resistors. Kinda trips off the tongue, donit?

[Leo_Gnardo]

Wow, you know, all these names are colorful and fun. In all my years, I never adopted a name for them, I still call them rectangular ceramic resistors. Kinda trips off the tongue, donit?

Better than the brand names I see on 'em: Xicon, Yageo. "Workman" on the old ones. I picture a sweaty guy with pick n shovel, what's he need a square cement resistor for? Hm, maybe he's the one mixing the mortar for a new batch.