Does anyone know the specs for the power transformer and a possible replacement in the UK.
I was just doing some tests on my amp and went to bleed the capacitors before finishing up but I hadn't turned it off and there was a fizzing noise and all went dead. Now I don't get any volts on any of the secondaries so I'm thinking the transformer has popped.
I was just doing some tests on my amp and went to bleed the capacitors before finishing up but I hadn't turned it off and there was a fizzing noise and all went dead. Now I don't get any volts on any of the secondaries so I'm thinking the transformer has popped.
For information:
I burned out the transformer on my A9
. A replacement from Duok was $80, shipped to the UK.bosch,
Prevent the "Surviving Spouse Syndrome".
Vacuum Tube Amplifiers Require Bleeder Resistors in the B+.
Safety First!
The most common mistake in schematics of tube amps is the lack of bleeder resistors.
Turning off the power, and then removing the IEC power cord connector does not make the amplifier safe.
Plan the RC time constant of your bleeder resistor and capacitance, versus the B+ voltage to discharge it to 42 Volts or less by the time you can take out the screws and remove the bottom cover.
No bottom cover?
Another "Surviving Spouse Syndrome"
Just saying.
Prevent the "Surviving Spouse Syndrome".
Vacuum Tube Amplifiers Require Bleeder Resistors in the B+.
Safety First!
The most common mistake in schematics of tube amps is the lack of bleeder resistors.
Turning off the power, and then removing the IEC power cord connector does not make the amplifier safe.
Plan the RC time constant of your bleeder resistor and capacitance, versus the B+ voltage to discharge it to 42 Volts or less by the time you can take out the screws and remove the bottom cover.
No bottom cover?
Another "Surviving Spouse Syndrome"
Just saying.
Last edited:
Thanks for the reminder 6A3sUMMER, I apreciate the amps potential to do me harm.
I have a magic wand which I use to discharge the caps, 100R resistor on a chop stick with a croc clip at one end which I leave on ground and use every time before my hand goes near the amp.
I think you're right though.... there's no substitute for bleeder resistors fitted to the amp. I think I'll be doing that before anything else.
I have a magic wand which I use to discharge the caps, 100R resistor on a chop stick with a croc clip at one end which I leave on ground and use every time before my hand goes near the amp.
I think you're right though.... there's no substitute for bleeder resistors fitted to the amp. I think I'll be doing that before anything else.
That's very tidy !! great work.
I ditched the PCB in mine but it's a rats nest next to yours.
https://www.diyaudio.com/forums/tubes-valves/268969-boyuu-el34-a9-tube-amp-114.html#post6247097
A9
if you look on the pcb of my amp just in front of the mains transformer you will see 2 resistors - the grey ones , these are 200k 2w and bleed everything off when powered down - my amp bleeds to 10v in about 15sec - then all is safe to go in there - they bleed off the 3 big caps
oh **** - i wonder if you could get one from primary windings that would fit nicely - and it would be a uk product !!For information:
I burned out the transformer on my A9
if you look on the pcb of my amp just in front of the mains transformer you will see 2 resistors - the grey ones , these are 200k 2w and bleed everything off when powered down - my amp bleeds to 10v in about 15sec - then all is safe to go in there - they bleed off the 3 big caps
Just for information, I changed the coupling caps to Russian PIOs and thought it was a backwards step. I have just used Auricap XOs and they sound amazing - so open.
I also rewired to triode but on my Frugalhorns it sounded too forward so back to UL. Really enjoying playing with this. Gonna try some KT77s next. Happy daze.....
I also rewired to triode but on my Frugalhorns it sounded too forward so back to UL. Really enjoying playing with this. Gonna try some KT77s next. Happy daze.....
A9
you can probably already work out ive changed everything from the original kit on the couplings i went for those big ERO 0.22 polyprop's - tubes im running gold lion kt77 - chatham Jan 5r4wga - and the pre amp tubes are otk russian 6h9c - i had some sylvania in there but so microphonic you couldnt get near them - speakers are klipsch r51 monitors 92db - i have also created the virtual centre tap groundings - all resistors are Amtrans 2w carbon - alps blue pot and better binding posts and input jacks - mine has zero humm , hiss etc - as its new and done about 20hrs now its going on the scope next week at vintagetech as i dont have one -
you can probably already work out ive changed everything from the original kit on the couplings i went for those big ERO 0.22 polyprop's - tubes im running gold lion kt77 - chatham Jan 5r4wga - and the pre amp tubes are otk russian 6h9c - i had some sylvania in there but so microphonic you couldnt get near them - speakers are klipsch r51 monitors 92db - i have also created the virtual centre tap groundings - all resistors are Amtrans 2w carbon - alps blue pot and better binding posts and input jacks - mine has zero humm , hiss etc - as its new and done about 20hrs now its going on the scope next week at vintagetech as i dont have one -
Nice!
Ooooooo.... You went with posh caps👍👍
What's the little terminal strip for?
A bleeder?
I put together something similar in the same spot.
Mine is a bleeder, doubling as a 45v potential divider to elevate the artificial center tap of the tube heaters and an led indicator for high voltage warning.
A9
The pair of 200k bleeders are the grey coloured ones in front of the mains transformer, they bleed off the 3 big caps , very quickly I might add , I might change the value of these ? They are 200k 2w but run bloody hot 🔥, the tag strip is where I made the artificial centre taps for both heater circuits , its the quietest tube amp ive heard in a long time regarding hum n hiss , its going on the scope Wednesday at a technician so I'll have the report on my 2nd built amp
The pair of 200k bleeders are the grey coloured ones in front of the mains transformer, they bleed off the 3 big caps , very quickly I might add , I might change the value of these ? They are 200k 2w but run bloody hot 🔥, the tag strip is where I made the artificial centre taps for both heater circuits , its the quietest tube amp ive heard in a long time regarding hum n hiss , its going on the scope Wednesday at a technician so I'll have the report on my 2nd built amp