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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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18th Oct 2009, 11:15 pm | #21 |
Retired Dormant Member
Join Date: Mar 2006
Location: Sheffield, South Yorkshire, UK.
Posts: 1,587
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Re: "Camms" one Valver
As Oerjan suggests you may need to increase the time constant of the grid leak. At these low frequencies the capacitor value should be higher. You need a time constant that is much longer than the RF cycle time to build up the bias.
The valve may not oscillate unless you operate it near cut off. Mike |
21st Oct 2009, 4:43 pm | #22 |
Retired Dormant Member
Join Date: Sep 2009
Posts: 487
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Re: "Camms" one Valver
I have a new Favorite Valve now, the ECC88!
what a fantastic little device I was having major problems trying to get SW to work using the ECC82, I`d long since given up on the 83 and the original #76 I was using, nothing less than 10 turns tuning coil would work and even then the rxn had to be turned all the way up just to get a peep out of a strong station. so I went through my triodes and noted that I had a dozen of these ECC88s, so I looked them up and it said VHF use, so I figured there`s no harm in trying and promptly rewired the heater to be compatible, happily the rest AKG were pin for pin. fired it up and a few seconds later there was Life! and not only that but it works down to 5 turns on the tuning coil I figured for a little extra boost I`d use the other triode as an antenna pre-amp, now it`s actually Very loud and working great! I`m listening to an American station right now as clear as Radio 4 |
21st Oct 2009, 4:59 pm | #23 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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Re: "Camms" one Valver
In Britain the ECC88 was mainly used in lab equipment like oscilloscopes, and isn't very common. It has recently found favour with the valve hifi people so if your valves are NOS you might want to consider selling them.
The PCC88 was a very common TV valve and is identical apart from the heater voltage. You find PCC88s rolling round in junk boxes all over the place. http://www.r-type.org/exhib/aai0011.htm http://www.r-type.org/exhib/aad0297.htm Your 'American' station may not be actually transmitting from the US. Many international SW broadcasters use relays all over the world. There are many fewer in Europe than there used to be but there are still plenty in Africa and the Middle East. Paul |
21st Oct 2009, 6:14 pm | #24 |
Tetrode
Join Date: Jan 2007
Location: Lincoln, Lincs. UK.
Posts: 94
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Re: "Camms" one Valver
Paul, just looked on that place and PCC88's are more expensive than ECC88's! The world's going mad!
Charlie |
22nd Oct 2009, 1:06 pm | #25 |
Octode
Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,698
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Re: "Camms" one Valver
This is a fascinating thread and it simply emphasises something I've thought for many years, namely that FJ Camm should have been knighted, or at least a film made about his life. The latter would be surely every bit as interesting as some of the recent 'Horizon' subjects!
-Tony p.s. My first set was a Camm one-valver, too. Brilliant man. |
22nd Oct 2009, 1:45 pm | #26 |
Retired Dormant Member
Join Date: Sep 2009
Posts: 487
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Re: "Camms" one Valver
I`v made a couple more mods to the circuit, that involved taking out the HF choke and replacing it with a transformer so that I can jack an Amp into it as those old phones are hard on the ears after several hours non-stop listening, as a result I had to alter the value of the rxn cap a bit too, but I can now use a 3 Turn tuning coil and can listen way up to 9 MHz+
as for the above post I couldn`t agree more |