Daddy Dee Posted September 7, 2005 Share Posted September 7, 2005 This certainly reveals my ignorance, but I've been wondering. What would we be dealing with here? Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted September 7, 2005 Share Posted September 7, 2005 NOOOOOOO........ yer gonna get in a lotta trouble ...!!!! ......[] major rework needed ... much more , i think, Heater Current .. Bias, Screen Resistors Quote Link to comment Share on other sites More sharing options...
sunnysal Posted September 7, 2005 Share Posted September 7, 2005 dee, the answer is no. a "rework needed" is an understatement! if you have one or the other stay with that and upgrade tubes to best NOS and upgrade caps in the amp...tony Quote Link to comment Share on other sites More sharing options...
sunnysal Posted September 7, 2005 Share Posted September 7, 2005 VhIhVaMaxVg2MaxVhkMaxPaMaxPg2MaxIkMax 6.31.5800500100258150EL34 Quote Link to comment Share on other sites More sharing options...
sunnysal Posted September 7, 2005 Share Posted September 7, 2005 6L6 VhIhVaMaxVg2MaxPaMaxPg2Max 6.30.936027019.02.5 Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted September 7, 2005 Author Share Posted September 7, 2005 merci Good advice to keep me out of trouble. Quote Link to comment Share on other sites More sharing options...
Marvel Posted September 7, 2005 Share Posted September 7, 2005 Dee, I have been told that with some minor adjustments that you can go the other way. Like put 6L6GCs into an ST-70. There would have to be some adjustments made, but there wouldn't be the load on the heater windings. Switching TO an EL34 would add almost two amps load on the heater windings (assuming two tubes per side). One of the guys on the DIYTube forum pust in 6L6 tubes instead of EL34 tubes on one of Shannon's boards. Maybe he used 6L6 tubes on the EL84 based amp. Added wires off the board and ran them to octal sockets instead of the pc mount 9 pin sockets. Then he had to make adjustments with the PS to have all the voltages split out correctly. Bruce Quote Link to comment Share on other sites More sharing options...
3dzapper Posted September 7, 2005 Share Posted September 7, 2005 I successfully converted one of my Scott 299Cs to EL-34s, switching the pinouts on the octal sockets as required. It is using the power transformer for 2 filaments and an additional small 12V torriod transformer for the remaining 2 in series. To limit power to the output transformers to approx 20 watts, the EL-34s are permanently strapped in triode mode. Sounds great I may add. Rick Quote Link to comment Share on other sites More sharing options...
djk Posted September 7, 2005 Share Posted September 7, 2005 Audio Research did a re-build of the ST-70 with the 6L6, but it is a big chore. Quote Link to comment Share on other sites More sharing options...
sunnysal Posted September 8, 2005 Share Posted September 8, 2005 The key here was "drop in" , in no way is it a drop in replacement. the amp has to be modded extensively. trannies, caps, resistors...so stay away from that idea...however good el34 amps can be found a low prices (ST-70 for example) why have both? regards, tony Quote Link to comment Share on other sites More sharing options...
DRBILL Posted September 8, 2005 Share Posted September 8, 2005 DD, I have a book (terribly worn) that I highly reccomend: Tube Substitution Handbook by William Smith and Barry Buchanan, now in the second edition 1998. Prompt Publications (a division of SAMS). ISBN 0-7906-1148-1. Antique Electronic Supply has them at $21.95. www.tubesandmore.com You need their catalog, too. DB Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted September 8, 2005 Author Share Posted September 8, 2005 Thanks all. Some very good info here. I am learning and actually like learning. Quote Link to comment Share on other sites More sharing options...
pauln Posted September 9, 2005 Share Posted September 9, 2005 Yes, it could be done. As an example, here is what you would need to do to replace the 6L6 with EL34 on a Fender guitar amplifier. The amp gurus in the forum may be able to connect the dots... and infer how to help you do it on your amp. Courtesy of Ken Fischer, Trainwreck Circuits; stolen from The Tube Amp Book 4rth Ed., by Aspen Pittman page 282 ================================================================================================= 1] Between pins 4 and 6 on each tube socket is a resistor, probably 470 ohm. Replace this with a 5 watt 1000 ohm resistor. 2] Between pins 1 and 5 on each tube socket will be another resistor, probably about a 1500 ohm. Disconnect the pin 1 end so it stands up bare ended and connect the other wires that went to the 1 pin to the standing up bare end of this1500 ohm resistor. 3] Connect pins 1 and 8 with a solid wire. 4] Increase the value of the resistor in series with the bias diode to reduce the bias voltage to obtain proper bias (this value will vary from amp to amp). NOTE: If you want to go back to the 6L6, just adjust the bias supply. Hope this helps, Paul Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted September 10, 2005 Share Posted September 10, 2005 NOOOOOOO ..! more heater current = Bad Power Xfmr, ............sooner rather than later on some lightly built stereo amps Quote Link to comment Share on other sites More sharing options...
Marvel Posted September 10, 2005 Share Posted September 10, 2005 NOOOOOOO ..! more heater current = Bad Power Xfmr, ............sooner rather than later on some lightly built stereo amps Hence my comment that it would be easier to go the other way ( EL34 to 6L6). I can only imagine that most older tube gear way a real cost/performance ratio and the power tranny was close to the limit already. Not everyone overbuilds. When it came to iron, the cost went up quickly. Still does. Bruce Quote Link to comment Share on other sites More sharing options...
sunnysal Posted September 10, 2005 Share Posted September 10, 2005 pauln is giving advice intended for a guitar amp, I would not try this on a home amp. it can overload the trannie (as mentioned before...), go buy a used st-70 man.... tony Quote Link to comment Share on other sites More sharing options...
NOSValves Posted September 11, 2005 Share Posted September 11, 2005 In a amp with adjustable bias like a ST70 a 6L6GC will drop right in and usually bias up perfectly. The pin outs of the two tubes are indentical and they both generally require the same amount of negative grid voltage for biasing and both have similar plate dissapation specs. Now a regular 6L6 or 6L6GB will not live very happily in the amp like a ST70 or similar. I'm not sure where anyone is getting the idea major changes are required. KT66's are another matter they genrally require a pretty gopod amount more negative voltage applied to the grid to get the bias down. They may need some bias circuit adjustment. Craig Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted September 11, 2005 Share Posted September 11, 2005 Dude ... did ya read ...???? 5881/ 6l6 amp to el34 gonna need an adjustable bias resistor ...... gonna need more heater current.......... this is true in guitar amps, where my knowledge comes from hi-fi amps aren't built nearly as tuff ... Quote Link to comment Share on other sites More sharing options...
Marvel Posted September 12, 2005 Share Posted September 12, 2005 I thought I was correct. The guy who added 6L6 output tubes to his EL84 amp pretty much only had to change the PS so the different voltages would be correct. He had a stout PS tranny on it, and swapped the 9 pin sockets an put in octals. But, yeah, going the other way will require a bit more care. Quote Link to comment Share on other sites More sharing options...
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