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In Reply to: RE: Favorite Tubes for DIY posted by Eli Duttman on June 29, 2008 at 06:56:24
Old 1940s era 7C5 are a great option for 6V6GT tubes that can be expensive.
Follow Ups:
Screen grid fragility makes the 7C5 awfully close to the 6AQ5.
Google El Leako to see a Leak Stereo 20 converted into an "El Cheapo" style amp. SHiFTY did some very nice work. He used 7C5s as the O/P tubes. ;> )
Eli D.
Google El Leako to see a Leak Stereo 20 converted into an "El Cheapo" style amp. SHiFTY did some very nice work. He used 7C5s as the O/P tubes. ;> ) > >
I tried to find a picture, but no luck. You can do a lot with a Stereo 20 - mine has PPP 6S4 outputs and an ECC40 driver!! Next one will go all-DHT. May use 1624 outputs for that, but you really need something thinner to fit the chassis. Maybe 7C5 outputs and 3a5 in. That should be tasty, but would need a preamp.
Andy,
SHiFTY posted some pictures in the "El Cheapo" saga. A direct link is provided below. Notice the "gorilla" of a filter choke that was added to the OEM "iron" set. IIRC, our "Kiwi" friend also posted photos over on DIY Audio.
The low mu and low gm of the 3A5 argue against it being used as a LTP. However, the amount of loop NFB needed here is low. Linearizing the O/P trafo is the principal target. Perhaps Williamson style circuitry using the 3A5 after the "concertina" phase splitter is indicated. You're the expert on DH types, not me. Is there a good sounding single, modest mu, small signal DHT in your "pile"? I'm thinking of a strange, but likely palatable, "cocktail". DHT voltage gain DC coupled to a (SIC) ZVN0545A "split load" phase splitter holds the bottle count down to a reasonable level.
Eli D.
Notice the "gorilla" of a filter choke that was added to the OEM "iron" set. > > >
Absolutely gross - destroys the look. Yuk!
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I don't use loop feedback.
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Morgan Jones has a clever rewiring scheme for the OPT to make it sound better - hard wires the secondaries for 4 ohms.
< < < Perhaps Williamson style circuitry using the 3A5 after the "concertina" phase splitter is indicated.> >
I like to have a balanced in option, so I use a diff pair with CCS under it. I use the ECC40 if I need more gain and only have room for one stage, or I rely on some gain in the preamp if I just use DHTs.
< < You're the expert on DH types, not me. Is there a good sounding single, modest mu, small signal DHT in your "pile"? I'm thinking of a strange, but likely palatable, "cocktail". DHT voltage gain DC coupled to a (SIC) ZVN0545A "split load" phase splitter holds the bottle count down to a reasonable level.> >
Not really - there are a few DHTs with higher gain but the plate resistance gets silly - see 1H5, 3a/142A, 3a/108, DC80, 826, 1G6G. No - the thing to do is just use three stages in the amp, like 01A, 10Y, 300b. It's a predictable combination but it sure as hell works! Andy
I did not know that about 7C5 marginal screens. I have run trioded 7C5s fairly hard with 340 volts plate & 35 ma plate current. I did not see a glowing screen as I always take a peek inside power tubes. Perhaps the difficult angle prevented that on the 7C5 due to large top getter.
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