View Full Version : 7591a vs. el34


shadiah
07-27-2010, 09:59 AM
I saw a comparison of 7591a tubes recently and they were using a Dynaco ST70 as their test platform. Does this mean that the el34 and the 7591a can be used interchangeably (perhaps with some mods)?

battradio
07-27-2010, 10:18 AM
The tube sockets would have to be rewired and 7591's don't work well in ultralinear mode , 6L6's or 5881 would be better in the ST 70

shadiah
07-27-2010, 10:23 AM
Thanks for the reply. Actually, I was thinking about the availability of "good" 7591a tubes for my Scott LK72 and wondered about modding it to use el34's instead. Good el34's are a lot easier to find!

bricktop
07-27-2010, 10:27 AM
EL34 uses 1.5A per filament, 7591 uses only 0.8A. So right off the bat, you'd be slapping an extra 2.8 amps on the 6.3V winding, prolly not a good thing to do. The new EH 7591 do sound quite good, if you can get them to fit.

el-37
07-27-2010, 10:50 AM
I saw a comparison of 7591a tubes recently and they were using a Dynaco ST70 as their test platform. Does this mean that the el34 and the 7591a can be used interchangeably (perhaps with some mods)?

I am curious- is it possible they were using an EICO ST-70- which is a 7591 amplifier?

mhardy6647
07-27-2010, 11:05 AM
EL34 uses 1.5A per filament, 7591 uses only 0.8A. So right off the bat, you'd be slapping an extra 2.8 amps on the 6.3V winding, prolly not a good thing to do. The new EH 7591 do sound quite good, if you can get them to fit.

'specially on a Scott power transformer! :-o

shadiah
07-27-2010, 12:18 PM
I am curious- is it possible they were using an EICO ST-70- which is a 7591 amplifier?

That could be true. Guess I was just hoping for an alternate choice for 7591's. I have a good set now, but who knows about the future?

BTW, is there a good source when I go to recap the old Scott?

mhardy6647
07-27-2010, 01:02 PM
The new production EH 7591A are perfectly OK; and the JJ's are OK, too, when their QC isn't an issue. I've got a couple of quads of them that haven't yet self-immolated.

For capacitors, the yellow Illinois caps are more than decent, inexpensive, and small (an advantage under the deck on the Scott amps, if'n you ask me).

sheltie dave
07-27-2010, 05:38 PM
There are tons of good 7591as these days.

soundmotor
07-27-2010, 07:23 PM
Re: EL34's on an amp originally w/ 7591's, at least 10 years back there was a dearth of good 7591's available. The market for used tubes was limited and NOS 7591's were market-priced like lobster. A buddy converted his idle Fisher 500C to EL34's. The case doesn't fit on it anymore but it has been in nearly daily use since and it sounds great. Would I bother with it now? No, as mentioned above, good 7591's are available. There does not seem to be any pressing advantage for this conversion.

sloober
07-27-2010, 08:04 PM
I recapped an LK72 last week. Very simple little unit. I used the JJ 7591a tubes as they are right against the transformers. EH will not fit. Get them and then look for old consoles on CL. I recently got Conn organ with 4 Westinghouse 7591a tubes. 1 was bad, But a deal for $40 not counting all the other tubes I got.

Sonance'84
07-27-2010, 11:12 PM
I recently got Conn organ with 4 Westinghouse 7591a tubes. 1 was bad, But a deal for $40 not counting all the other tubes I got.

I'm looking for Westinghouse 7591's, and there happens to be a working Conn organ in my area for a decent price. I'm going to look at it tomorrow...I was wondering what model organ you found those in?

The lady couldn't find a badge or model number on it , so I'm not sure what she has. She said it has tubes, it gets loud and it's a two tier organ.

Thanks, Cory

shadiah
07-28-2010, 08:44 AM
Thank you for all your help. This is my first rebuild project. I bought it used in '77 form the guy who built it back in '65. I loved it when it worked! I run it without the cover (love the blue tube glow!).