Hiwatt build voltage issues

Vox and Hiwatt Discussion

Moderators: pompeiisneaks, Colossal

User avatar
xtian
Posts: 6990
Joined: Mon Apr 19, 2010 8:15 pm
Location: NorCal
Contact:

Re: Hiwatt build voltage issues

Post by xtian »

Your measurements sound OK. I can't explain the high voltage on the PI plates. Is any part of the circuit working? If you put a sine wave into the input, do the first few stages amplify?
I build and repair tube amps. http://amps.monkeymatic.com
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

Well this one has me shaking my head.. I just once again traced the circuit thinking I had to have missed something but all appears right..I am a novice at this stuff and this is only my fourth amp build and the only one so far that has given me fits.. I don't really understand how to introduce a sine wave.. Is that something I would need an oscilloscope for?
I brake for Lard......
User avatar
pompeiisneaks
Site Admin
Posts: 4222
Joined: Sat Jan 14, 2017 4:36 pm
Location: Washington State, USA
Contact:

Re: Hiwatt build voltage issues

Post by pompeiisneaks »

you need the oscilloscope to read it, but you can use a phone app, there are several for android and I'm sure there's some for apple as well, just look for function or signal generators.

If you don't have a scope you can build a signal listening device here's at least one video that shows the process:


Then you can listen for where the sine wave exists and where it may disappear.

~Phil
tUber Nerd!
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Re: Hiwatt build voltage issues

Post by Stevem »

If like you have posted in your chart that the bias voltage on pin 5 of any output tube is -61 volts then that why your voltages thru the rest of the amp are so off the mark!

Your output tubes are not even idling with -61 volts on pin 5 to load down the power supply!

Bring that down to -42 and see how your high voltages drop down to more normal levels!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

Stevem wrote: Thu Sep 14, 2017 10:47 am If like you have posted in your chart that the bias voltage on pin 5 of any output tube is -61 volts then that why your voltages thru the rest of the amp are so off the mark!

Your output tubes are not even idling with -61 volts on pin 5 to load down the power supply!

Bring that down to -42 and see how your high voltages drop down to more normal levels!
I adjusted the bias on my tubes and remeasured volts on the pins.. here is my latest voltage chart ( measured volts in bold).. most voltages are close and voltage on the 5 pin is now -40v ... unfortunately the volts on v4 plates are still over 400vdc
You do not have the required permissions to view the files attached to this post.
I brake for Lard......
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Re: Hiwatt build voltage issues

Post by Stevem »

Going back to where you had 491 volts on the output tube plates , this would infer that your AC input to the recto bridge was 350 volts on each leg, is this about what you have if the power tubes are yanked out?
I think it's just time to plug in and play it!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

Stevem wrote: Fri Sep 15, 2017 12:35 pm Going back to where you had 491 volts on the output tube plates , this would infer that your AC input to the recto bridge was 350 volts on each leg, is this about what you have if the power tubes are yanked out?
I think it's just time to plug in and play it!
Besides the high voltage on the PI plates I have no sound as well... but I am getting closer :|
I brake for Lard......
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Re: Hiwatt build voltage issues

Post by Stevem »

If you hook up a voltmeter set for AC volts across the output of the PI ( output tube side) and play thru the amp do you read voltage, like over 20 vac?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

Stevem wrote: Fri Sep 15, 2017 4:20 pm If you hook up a voltmeter set for AC volts across the output of the PI ( output tube side) and play thru the amp do you read voltage, like over 20 vac?
Being the electronics novice that I am. Could you be mores specific as to where I would place my probes... I really appreciate the help...
I brake for Lard......
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Re: Hiwatt build voltage issues

Post by Stevem »

The PI plates have coupling caps feeding pin 5 of the output tubes, hook your probes up the output tube side of those two caps.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

Stevem wrote: Sat Sep 16, 2017 10:52 am The PI plates have coupling caps feeding pin 5 of the output tubes, hook your probes up the output tube side of those two caps.
If I follow you correctly I put black probe to ground and red probe to output tube side of the coupling cap and I get 120vac on each cap. Strumming the guitar has no affect on the voltage. checked voltage on both sides of the caps and the volts are the same.. I get no sound and wonder if my OT is bad although I get 450vdc on the OT center tap and the primary's on the 3 pins of the power tubes also have volts?
I brake for Lard......
Stevem
Posts: 4551
Joined: Fri Jan 24, 2014 3:01 pm
Location: 1/3rd the way out one of the arms of the Milkyway.

Re: Hiwatt build voltage issues

Post by Stevem »

No, not from each cap to ground, across each cap!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

Stevem wrote: Sun Sep 17, 2017 11:05 am No, not from each cap to ground, across each cap!
Measurement across the caps while strumming is 6.2vac ... What am I looking for that to tell me? Thanks Steve!
I brake for Lard......
sluckey
Posts: 3062
Joined: Sun Jul 22, 2007 7:48 pm
Location: Mobile, AL
Contact:

Re: Hiwatt build voltage issues

Post by sluckey »

I think you should concentrate on the high voltage on V4 pins 1 and 6. Until that is fixed you will not get any sound through this amp. Measure the voltage directly across the 91K and then the 82K plate resistors (meter leads directly on the leads of each resistor). If the voltage is zero or very small, then the tube really is not conducting. A likely suspect would be that the cathode circuit has no path to ground.

Next, turn the power off and measure the resistance from V4 pins 3/8 to chassis (one probe on chassis, the other probe directly on the socket pin). Do you get approx. 22KΩ? If you get a much higher reading start tracing the path from pins 3/8 to ground. One likely suspect would be a missing under-board jumper between that 22K and 2.2K resistor.
User avatar
playonit
Posts: 241
Joined: Sat Nov 10, 2007 5:32 am
Location: Hamburg, NY

Re: Hiwatt build voltage issues

Post by playonit »

sluckey wrote: Sun Sep 17, 2017 2:27 pm I think you should concentrate on the high voltage on V4 pins 1 and 6. Until that is fixed you will not get any sound through this amp. Measure the voltage directly across the 91K and then the 82K plate resistors (meter leads directly on the leads of each resistor). If the voltage is zero or very small, then the tube really is not conducting. A likely suspect would be that the cathode circuit has no path to ground.

Next, turn the power off and measure the resistance from V4 pins 3/8 to chassis (one probe on chassis, the other probe directly on the socket pin). Do you get approx. 22KΩ? If you get a much higher reading start tracing the path from pins 3/8 to ground. One likely suspect would be a missing under-board jumper between that 22K and 2.2K resistor.
Measure voltage on each resistor - both leads on 91k and then both leads on 82k ? meter set to DC or AC? - Thanks
I brake for Lard......
Post Reply