Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ALBATROS1234 on November 07, 2023, 07:14:53 am
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A couple years ago I bought a "lot" of radios from this guy on FB. There were a couple of philco 60 chassis that had been gutted. PT worked, although I had to strip off the Bell ends and put new wires on because they were crumbling. So I had the bright idea that I was going to build a guitar ramp using 1930s tubes. I have a 77 which is the predecessor of a 6j7 and 6sj7 into a 75 which led to the 6q7 and later the 6sq7 and the power tube I was using is a 42 which is basically a 6f6g. Of course it has a 80 rectifier. Kind of got it together it needs some tonal tweaks but it sounds fairly decent and I assume we'll end up being a really nice cleanish blues machine. My question is there any other six pin tubes from that era that give more power. I know about a 41 but that's a 6k6 and it's a weaker tube. I'm just trying to get more volume and do not want to start changing sockets. Any ideas?
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I built a similar amp from Philco 1936 Car radio "Phirty6"
84 rectifier, 77(as triode) to 75 to 41. My first grid on top cap tube amp. Sounds pretty decent.
Its really quiet because all the signal lines are separated by the chassis from the AC and DC lines
Planning to add all pentode channel soon...
https://el34world.com/Forum/index.php?topic=29688.msg326827#msg326827
Have another uncompleted with Push Pull 42 that is in work "Prew42"
https://el34world.com/Forum/index.php?topic=29232.0
Cannot find an alternative to either 41 or 42. Let me know if you do find something
Maybe try ARF at https://antiqueradios.com/ or
http://www.nostalgiaair.org/ or
https://www.radiomuseum.org/
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Thanks for your reply. Yea I love to mess around with different stuff just to see what tones will seep out. First I found I really like octal preamp tubes I have a few 6SJ7 designs and . Don't get me wrong I have some really sweet 12AX7s but I have played around quite a bit with pentode preamp tubes and pentode triodes like 6U8a. I actually like 6F6g tube tone on some of my designs but they are usually close maybe 3/4 or better to 6v6 volume. I know that's what a 42 is supposed to be but it just seems underwhelming in volume. I looked around and then thought maybe there is a 6 pin power tube I don't know about and I should post. I hate to change the socket from a 1935ish chassis if there is a 30's power triode that puts out more volume. Worst case I will have to try a PP set up. I should be able to get decent vol from 2.
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807 is sure of that vintage and was the father of the 6L6. 307 is rarer but similar.
813 is nominally 7 pins plus a plate cap but two are NC. Six? (The socket is "Giant 7-pin", which stayed popular in ham radio for many decades.) A pair of 813 in push-pull AB1 will do 250-500 Watts sine audio.
You may well be limited by your power transformer, and possible OT impedance. Obviously push-pull needs at least twice the supply current and you may not free-up that much by scrapping the tuner.
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Thanks PRR, I was trying to use the socket that is on the chassis. The 42 it came with is a 6 pin. Filament current wise I did eliminate the 6A7 so I can possibly use that for a 807 which as I understand is basically a 6L6G with a grid cap and I suppose I could try to do a push pull 42 but I was trying to keep it single ended because I am not sure what the transformer can bear. I did find a tube the other day that shows some promise I have to do a little research to verify if it would give me more power as I suspect it will and that's the 6B5 which I'm sure you know is a direct coupled triode with a driver and a power stage it says it makes 4 to 6 Watts of power in the my late 30s Sylvania tube manual . I think a 42 which is a 6f6g with a different base would probably only make three to four Watts Max so it may be a slight volume increase. I tell you what though those old 30s and 40s radio tubes have a totally different sound than a 12ax7 preamp. Much more grit and girth
Octals are like that too when used as preamp tubes, that's what gave me the idea I've built several all octal amps which I love the raw lofi tone.
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.... 6L6G with a grid cap ....
No, it is a Plate Top Cap
Franco