Hi, Attached is Cayin A55-t tube amp schematics.
I try to put el34 , able to get a bias current (0.4 V ~ 40mA) and make the el34 singing on place of 6550.
The problem is when i turn off the amp, there is weird crackling sound from the tube.
What are the thing that cause this ? are the b+ (430V) is too high for el34 and is not suitable ? or are there another thing that cause this ?
The other thing is what are the theory behind power tubes screen grid resistor 47k ? for safe on fly transition between ultralinear and triode mode?
I try to put el34 , able to get a bias current (0.4 V ~ 40mA) and make the el34 singing on place of 6550.
The problem is when i turn off the amp, there is weird crackling sound from the tube.
What are the thing that cause this ? are the b+ (430V) is too high for el34 and is not suitable ? or are there another thing that cause this ?
The other thing is what are the theory behind power tubes screen grid resistor 47k ? for safe on fly transition between ultralinear and triode mode?
I have a Heathkit amp that does that. Is it a sort of "tinkling" noise? I always assumed it had to do with the filament/cathode contracting as it cooled.
BTW, I assume you replaced both power tubes with EL34s, and not just one? In a push-pull amp it is important that the output tubes be reasonably well matched. Obviously a 6550 and an EL34 are fairly different tubes.
BTW, I assume you replaced both power tubes with EL34s, and not just one? In a push-pull amp it is important that the output tubes be reasonably well matched. Obviously a 6550 and an EL34 are fairly different tubes.
Hi Petertub, the amp has little brother variant which use el34 , i just want to able to switch sound.
yes, h317 it’s thinkling sound, btw i replace all the tube. just the sound too loud too ignore, do nt know which component to replace to re,more ve the noise
yes, h317 it’s thinkling sound, btw i replace all the tube. just the sound too loud too ignore, do nt know which component to replace to re,more ve the noise
I wouldn't necessarily worry too much about it. I've heard a few amplifiers that do that. What brand of EL34 are you using? Did the 6550s do it as well?
430V is not too high for an EL34. Heathkit ran nearly 500 in the AA-121, and the spec sheet says it can take up to 800 (I wouldn't push it that hard though). At 40 mA with that B+, you should be fine. That comes out to 17.2W of plate dissipation, which is well within the 25W limit of the EL34.
430V is not too high for an EL34. Heathkit ran nearly 500 in the AA-121, and the spec sheet says it can take up to 800 (I wouldn't push it that hard though). At 40 mA with that B+, you should be fine. That comes out to 17.2W of plate dissipation, which is well within the 25W limit of the EL34.
I've heard funny noises from power tubes also when powering off. I say go for it and as long as the tubes your installing will bias up go ahead and listen to the amp and see if you like the differences you are hearing. If the bias will go down far enough I would also try some 6L6GC's or 6BG6GA with socket adapters.
There is one difference between the EL34 and other power output tubes like the 6550 : the grid 3 is not connected internally to the cathode therefor you MUST make the connection outside between pin 1 and 8 : http://www.jj-electronic.com/images/stories/product/power_tubes/pdf/el34_e34l.pdf
I have done that in the EL34 Baby Huey, see the shematic in post 1 : EL34 Baby Huey Amplifier
Marc
I have done that in the EL34 Baby Huey, see the shematic in post 1 : EL34 Baby Huey Amplifier
Marc
are this the reason behind the thinkling noise?
what are negative bias voltage required here ? i get about -50 ~ -70 v on the bias voltage.
what are negative bias voltage required here ? i get about -50 ~ -70 v on the bias voltage.
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