• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Another 6L6 schematic

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
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I will warm up my soldering iron and try some stuff.

I would like to inform that for 1. I never got instability. For 2. I have 12AT7 to try, must see for a tail source scheme. For 3. I don't get clipping before power output is exhausted in insensitive speakers, maybe its the 8.2K 6L6GC gridstopper I use that helped me?
 
sorenj07

sorenj07

Member
Joined 2006
OK, here's where my project stands so far.

I'm probably going to full-wave rectify a 282X (500-0-500 200mA) with some NOS 5U4GB's I got, with choke input (193J 10H 82R 200mA). After that, I'm having some trouble deciding what to do. I just got 4 80uF 370VAC motor caps which I'd like to use, and I have two 500uF 500V JJ capacitors.

Some problems, though. The only way I can seem to get PSUDII to not dip the voltage below 0 is with 80uF at the first LC, and 18uF for all PSU caps after that. The second choke I'm using is the 157J, 10H 65mA 205 ohms.

Does anyone have any suggestions? I suspect that PSUDII is giving me these errors erroneously because the warm-up time of a 5U4GB is a lot longer than 1 second, besides other things, but I'm somewhat disconcerted about the little notifications about "current sinks pulling voltage below 0"...

Other possibilities for the capacitors include using two paralleled per monoblock in the first LC, providing 160uF to the OPT's, leaving the 18uF Solens for the rest. Another option is to use an 80uF motor cap in the first two LC filters. I could also try mounting the 500uF caps somewhere... What do you think?
 
sorenj07

sorenj07

Member
Joined 2006
No, this is a cut-and-dried choke input filter. I've decided to parallel the 80uF motor caps after the choke, and use two 22uF 630V Solen caps paralleled after the second choke, which I've changed to the 9H 40mA 300R 157G due to 2" space constraints. I also change the two input stage resistors to 19K 1W and 29K 1W due to the increased voltage drop after the choke. the caps after those resistors remain 18uF 400V Solens.

I'm still tripping the negative-voltage error in PSUDII but am pretty much disregarding it, because as long as I don't blow the 5U4GB, I don't see at all how the relatively low capacitances could ever hurt the 282X transformer.

Parts to finish the amp come out to $450 so I'll be sitting around for a little while until that money magically appears... wish me luck :)
 
sorenj07

sorenj07

Member
Joined 2006
wow, that just about makes my day. i'll still go the route of all film caps in the PSU but it's nice to know that when designing other things in the future, I will have more freedom than expected :). this weekend i'll probably be picking up a PP 6V6 hammond organ amp that i'll do something to, but that's for another thread (pics, anyone? :D)
 
sorenj07

sorenj07

Member
Joined 2006
Well, the organ amp was a bust (I'm young enough to have to deal with my parents for these matters). Anyway I also realized that my 6L6WXT+'s probably won't be able to take 450V on the plates and screens... My PSU can put out 450V into 120mA per channel for the power tubes, probably more (200mA PT, 200mA choke, 5U4GB) so I was wondering if I should pick up a pair of 6550's or something instead of the 6L6GC's.

I haven't bought the parts with which I would bias the output tubes so I assume that I could mess with the resistance to let the Williamson's input stage swing the required volts?

My OPT is 6600 ohms anode to anode and can handle 60W. Should I go for the 6550's? El34's? KT-88's (except for money)? Are there other big tetrodes or pentodes I should try? I guess I'm open to many suggestions here, which is probably well worth the price of the $45 spent on a quad of the WXT's...
 
J

jon_010101

Member
Joined 2005
sorenj07 said:
Anyway I also realized that my 6L6WXT+'s probably won't be able to take 450V on the plates and screens... My PSU can put out 450V into 120mA per channel for the power tubes, probably more (200mA PT, 200mA choke, 5U4GB) so I was wondering if I should pick up a pair of 6550's or something instead of the 6L6GC's.
Click to expand...

I've briefly used those tubes at that operating point and they actually do Okay if they are properly matched. But I ultimately fried mine in a multimeter-misconnection incident. :hot:

Good 6L6GCs won't mind that operating point. And, a good quad of Chinese KT66's can handle 450V @ 60mA just fine. But they cost almost as much as 6550s.

A "money" tube to consider, however, is... ...

...like Wavebourn, I'll email you. :smash:
 
Wavebourn

Wavebourn

Member
Joined 2006
wavebourn.com
sorenj07 said:
lol thanks, i'll check the email. i was tempted by an offer on local Craigslist for a matched quad of Chinese GC's for $30 but I figured... 6550's or KT-88's could put out a lot more power, which my setup can clearly support, so why not?
Click to expand...

Quad of 6P3S-E gave me 80W with 375V plate/310V second grid, 4K CT transformer, 40 MA per tube bias. Some sellers claim they are 6L6-GC, but I am afraid to load them harder. However, if Tubelab tortured them and found as good as GC... :cool:
 
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