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SEP EL-34 to 6L6GC?

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I bought a EL-34 SEP Chinese amp and was wondering what I need to do to be able to run 6L6s in it as well. I know it can be done, but don't have a clue about what I need to do with pin #1 for the 6L6 and if I need a switch. I have seen an amp that would run 6L6s and EL-34s but it has been so long ago that I can't remember anything about it other than it sounded great.

Thatch
 
It came with a simple schematic that did not have any voltages on it except for cap values. pins 1 and 8 show to be hooked to the cathode, but only 8 is hooked to outside wires. I am going to have to pull this thing apart and eyeball the stuff. The amp is really generic, if fact the brass plate said Tube and under that Vacuum Tube Amplifier. I think I found a wholesaler, but they sold me a single unit. It sounds very good as is though I have retubed it. Mullard EL-34s, an RCA fat bottle 5AR4 and Telefunken 12AX7s. I am just going to have to see pin one on the EL-34s and then find out what my options are.
There are 4 amps on the rectifier and the heaters for the power tubes is 3.5A for the pair. Heaters are not shown on the schematic.
In the PS there is a 3H choke that is 200mA and next is B1 for the OPTs. The OPTs have like an ultralinear tap that has a 100 ohm resister going to pin 4 (grid) and the plate has nothing in line between it and the top of the OPT. Plate and screen in Class A both call for 250V and a 2K load.
I can try to scan what I have, but without voltages it might not be as helpful as you need.
Thatch
 
I think I got it. This is all I got with the amp.
 

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I think I got it. This is all I got with the amp.

Hi,
look at the data sheets. The 6L6GC is not the same as a EL34. They are total different type of tubes. A EL34 is a real pentode and a 6L6GC is a tetrode. You may plug a 6L6GC in and it will play music. But a circuit designed for a special kind of valve perform best only with the one which its designed for.

73
Wolfgang
 
I bought a EL-34 SEP Chinese amp and was wondering what I need to do to be able to run 6L6s in it as well. I know it can be done, but don't have a clue about what I need to do with pin #1 for the 6L6 and if I need a switch. I have seen an amp that would run 6L6s and EL-34s but it has been so long ago that I can't remember anything about it other than it sounded great.

Thatch
Why ?? There is no shortage of EL34, and they usually are cheaper then 6L6GC( 6L6 won't stand the power )
Do you honestly think that replacing the intended tube with a different one would be of any benefit ?
 
Aside from the fact that there probably isn't anything to be gained by subbing a 6L6GC for the EL34 it can be done but you might have to change R107/8 & C103 etc. You'll learn something if nothing else and it's fun mucking about with toooobs.

As we don't know what the OPT pri Z is it will be a bit tricky to draw a loadline but have a look at the 6L6GC datasheets and make a guess if after popping in a 6L6 and it doesn't sound right.

Andy.
 

PRR

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I too don't see why it needs changing.

It will almost-certainly work, as good as it does now. It isn't working the power tube to its limits or leveraging the small differences. In "fixed" bias you usually need to tweak the negative bias, but in self (cathode) bias it will usually find a happy operating point. (I have used exactly that 500r value, halved, in a 2-tube amp that ran fine with any two of EL34 6L6GC 7027 6550/KT88).

My only concern is that pin 1 is G3 in EL34 but "Metal Shell" in 6L6. Because metal shell (or base) 6L6 are now rare, it does not matter. However if you do get a 6L6-type with exposed metal, the metal will be up at about +29 Volts. Not real lethal, no. But if you drop a hunk of metal in there (or use bear-claw tube base grips), it will short-out the bias and the tube will die quickly. I had a trick to allow this (also the 7027's different pinout) but if you "don't have a clue" then nevermind. The odds of you finding metal 6L6 or working 7027 are teeny.
 
Usually the bigger issue is putting EL34s in a 6L6 amp since a lot of 6L6 amps use that pin as a tie point. You don't want to tie the suppressor grid to the +450V supply...

The main problem with subbing 6L6s into an EL34 amp is that the 6L6 has a more anemic cathode/filament than the EL34 and is thus designed for a higher plate load. It will probably work, but it is sub-optimal.
 
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