Amp seems to work perfectly well, being repaired for minor problem, no succeptibility to microphony or tinging distortion. Testing the 2x EL34, gains are good and matched but after a minute on heated C/H insulation check, the resistance gradually decreases to 1M for one and 0.5M for the other. What problems will this lead to if continued use, and how quickly ?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
It means that the tubes are not precisely matched. Sadly, "matching" tubes these days is typically based only on "gain" and done for a quick claim to inflate prices.
No problems if each tube has an individual bias adjustment, and you watch over it. Even if they are biased together and that bias is attended-to, there should be no problems. How many hours on these tubes and are they driven to extremes or not?
What are you testing with?
Peter Wieck Wyncote, PA
on
It means that the tubes are not precisely matched. Sadly, "matching" tubes these days is typically based only on "gain" and done for a quick claim to inflate prices.
No problems if each tube has an individual bias adjustment, and you watch over it. Even if they are biased together and that bias is attended-to, there should be no problems. How many hours on these tubes and are they driven to extremes or not?
What are you testing with?
Peter Wieck Wyncote, PA
Unknown age, matched GT tubes, no date on tubes used by a pub rock band tested on Avo CT160
OK... Attend to the bias to the extent possible, and suggest that they travel with a spare set of tubes. If you have a new 6CA7/EL34 to test against, try that just to make sure you are not too far off.
At least you are using one of the very few testers that actually gives reliable information.
Peter Wieck Wyncote, PA
OK... Attend to the bias to the extent possible, and suggest that they travel with a spare set of tubes. If you have a new 6CA7/EL34 to test against, try that just to make sure you are not too far off.
At least you are using one of the very few testers that actually gives reliable information.
Peter Wieck Wyncote, PA
This one was used by REME Wing Hebrides in 1984
on
Huh, he is talking about heater to cathode leakage. Nothing to do with matching the tubes. The amount of leakage you have is no big deal for power tubes, if it gets below 100K then have a hum problem.
for
on
That was the sort of info I was after. I was wondering if there could be some sort of thermal runaway situation. I'd not noticed any hum but will make a point of trying to measure it for later reference purposes.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
for
on
Measured no more than 1mV rms hum over 4 ohm output for this one , level set for 2.25 W of 400Hz output, but disconnected and monitoring for shorted input
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.