I used 6DQ5s as fast RT pulse gens in the late 50s on magnetic cores in a memory research project. We needed fast rise time, these made 1.5A into 50R transmission lines, RTs were in the nanosecs. Driven by EFP60 secondary emission pentodes.
Somebody actually built an amp using EFP60s as the driver stage. The EFP60 has a very large gain/BW number, makes a great driver.🙂
Somebody actually built an amp using EFP60s as the driver stage. The EFP60 has a very large gain/BW number, makes a great driver.🙂
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those 6W6 tubes (and the equivalents) sure do sound great when run at more usual voltages, I've not pushed them hard but triode connected they are fantastically linear.
The L6 versions are rated at 200 volt plate, whereas the W6 versions are rated at 330 for vertical sweep service. That is, putting out full signal continuously, not idling at rated Pdiss. Same part, different ratings for different service. You just have to keep the plates at 200 or 250 if you’re going to let them sit there and cook. In those old radios, they saw 120-160 volts. I bought a bunch of 12W6 to experiment with, including rewiring a hot chassis 50L6 amp for parallel heaters and an isolation trafo. I may get to all that if CO19 goes on too long.
That is the key. In TV sweep service the tubes are running at full tilt all the time. You can't "turn down the volume" on sweep, so it's always putting power into the load. The two 6W6 failures both ran at around 300 volts in triode, and the idle dissipation was around 9 watts. 2 out of 3 tubes blew up at idle. One ran fine forever......until I switched to 6V6's which did fine in the same circuit but at a higher load impedance.
So a short update:
I think it was a bad connection to the biasing board.
I've rebuilt the amp using 50VA transformers for 3k load instead of 1k3, and 6DQ6B while I wait for 6P31S.
The PI had an error. The splitter should have used 47k on the plate and cathode, not 22k.
For the record, the 6DQ6B is rated for a 1M grid leak as max, I'm using 470k now.
Also, my 6P45S monoblocs are using 510k grid leak and have worked for a long time now... The VA driver is designed for for a 330k load so no problem there.
Time will tell I guess...
I think it was a bad connection to the biasing board.
I've rebuilt the amp using 50VA transformers for 3k load instead of 1k3, and 6DQ6B while I wait for 6P31S.
The PI had an error. The splitter should have used 47k on the plate and cathode, not 22k.
For the record, the 6DQ6B is rated for a 1M grid leak as max, I'm using 470k now.
Also, my 6P45S monoblocs are using 510k grid leak and have worked for a long time now... The VA driver is designed for for a 330k load so no problem there.
Time will tell I guess...
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OK, perhaps it was a bad 6DJ8, but with them I had a nasty 6-10kHz oscillation just loud enough to hear. I swapped them out for 6N1P and no more oscillation.
Also forgot to mention:
The 47uF decoupling caps for the phono and line stages were upgraded to 220uF.
Also forgot to mention:
The 47uF decoupling caps for the phono and line stages were upgraded to 220uF.
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