50 watt home build doesn't like 120v!

For those building and repairing amps on their own. Learna and share ideas.

Re: 50 watt home build doesn't like 120v!

Postby tracynorton on Fri Apr 15, 2016 6:20 pm

sigh....and did you check the EF86s for microphonics? :bday:
tracynorton
Knight
 
Posts: 1356
Joined: Sat Nov 29, 2003 8:01 am
Location: Peenemunde CA


Re: 50 watt home build doesn't like 120v!

Postby grasshopper on Sun Apr 17, 2016 11:27 pm

I reseated all the tubes and switched the power tubes around and it started working again :rawk: . I took the voltages with the amp at 75v, volume on both channels down with no test signal, plugged in to a dummy load (8 ohms). I made a spreadsheet for taking the measurements so it goes pretty quickly. Should I be testing with a signal?

I kind of rushed to get the schematic out. If there are errors my apologies.
Image
grasshopper
Peasant
 
Posts: 29
Joined: Tue Jan 26, 2010 9:57 am

Re: 50 watt home build doesn't like 120v!

Postby grasshopper on Tue Apr 19, 2016 1:28 am

tracynorton wrote:sigh....and did you check the EF86s for microphonics? :bday:


I tested the tubes with chopsticks and none of them seem to be microphonic. I paid special attention to the EF86's and didn't get any lingering tones out of the amp after tapping them. Just the sound of the actual tap carried through, then nothing.
grasshopper
Peasant
 
Posts: 29
Joined: Tue Jan 26, 2010 9:57 am

Re: 50 watt home build doesn't like 120v!

Postby pdf64 on Tue Apr 19, 2016 8:18 am

Your schematic looks very well drafted!
Unfortunately I may not be seeing the full picture, as the right hand side may be missing, eg no phase splitter.
Any progress on the ideas I suggested?
My band:-http://www.youtube.com/user/RedwingBand
pdf64
Knight
 
Posts: 1242
Joined: Thu Dec 14, 2006 9:55 am
Location: Staffordshire UK

Re: 50 watt home build doesn't like 120v!

Postby housekustoms on Tue Apr 19, 2016 6:35 pm

Unit_1 wrote:I threw this pic in to show it from a different angle, plus I just really loved this amp. Traded it for a guitar. Those Astron paper in oil caps are very hard to find and cost an arm and a leg but are worth it. These are the quietest caps I've ever used, so quiet you can't even tell which is the foil end on a audible cap tester I built. I bought 110 of these for a buck each on eBay from some guy that didn't know what he had, lol..

Hey! That 5e3 chassis looks very familiar... :whistling:

pdf64 wrote:Your schematic looks very well drafted!
Unfortunately I may not be seeing the full picture, as the right hand side may be missing, eg no phase splitter.
Any progress on the ideas I suggested?

Here ya go...click the thumbnail for a full size jpg image.

Image Click for full size image
I'm a little bit :old: now, but I still like to :jam:

Image
housekustoms
Page
 
Posts: 261
Joined: Fri Aug 26, 2011 12:43 am
Location: Tennessee

Re: 50 watt home build doesn't like 120v!

Postby grasshopper on Wed Apr 20, 2016 1:39 am

pdf64 wrote:Try swapping over the opposing polarity signals at any one point in the balanced part of the power amp, eg wires to power tube control grids, OT primary wires to power tube plates.


I tried swapping the tube control grids and the problem persisted. When I swapped the OT primaries the amp (amp itself, not the speaker) started making that high pitched sound, with no output to the speaker.
grasshopper
Peasant
 
Posts: 29
Joined: Tue Jan 26, 2010 9:57 am

Re: 50 watt home build doesn't like 120v!

Postby pdf64 on Wed Apr 20, 2016 7:31 am

I don't see that a full voltage survey at 75Vac mains is super useful, as the tube heaters are probably not hot enough to achieve the intended cathode emission.
So I suggest to keep it at full line voltage, now we know that the amp isn't drawing fault current.

grasshopper wrote:the amp is still making the same sound when I turn it on

Have you got a recording of this noise?

Have you checked it out on the scope, eg frequency, waveform, amplitude?

Is the sound from the amp in the previous clips via a free standing speaker chassis? If so, have you got a speaker mounted in a cab to use instead, for the recording at least?

Does the noise stop if you remove any pre-amp tubes other than the phase splitter? If not, how about if the phase splitter is removed?
My band:-http://www.youtube.com/user/RedwingBand
pdf64
Knight
 
Posts: 1242
Joined: Thu Dec 14, 2006 9:55 am
Location: Staffordshire UK

Re: 50 watt home build doesn't like 120v!

Postby grasshopper on Fri Apr 22, 2016 4:06 am

pdf64 wrote:I don't see that a full voltage survey at 75Vac mains is super useful, as the tube heaters are probably not hot enough to achieve the intended cathode emission.
So I suggest to keep it at full line voltage, now we know that the amp isn't drawing fault current.

grasshopper wrote:the amp is still making the same sound when I turn it on

Have you got a recording of this noise?

Have you checked it out on the scope, eg frequency, waveform, amplitude?

Is the sound from the amp in the previous clips via a free standing speaker chassis? If so, have you got a speaker mounted in a cab to use instead, for the recording at least?

Does the noise stop if you remove any pre-amp tubes other than the phase splitter? If not, how about if the phase splitter is removed?


I'll take some videos of the scope and freq of the hum soon. I uploaded a video of the different tube configurations you asked about and took new voltage measurements at 120v, with the bias at ~39mV (a bit hot, I know). For these tests I went ahead and unplugged from my bench speaker, and plugged into a 2x12 cab I built for this amp with celestion heritage G12H greenbacks. The cab is known to be good.

The youtube video is here https://www.youtube.com/watch?v=00PKaOYGWk8&feature=youtu.be

and the image with updated voltage measurements (@120v) is here http://oi64.tinypic.com/e9ugxy.jpg
grasshopper
Peasant
 
Posts: 29
Joined: Tue Jan 26, 2010 9:57 am

Re: 50 watt home build doesn't like 120v!

Postby BennJoltes on Wed May 25, 2016 6:23 pm

Hello everyone..i am new here and by profession i am a hardware design engineer. As per my experience instead of measuring mA you put a 1% 1 Ohm resistor in between tube ground and ground. Then you set your multimeter to mV, hook the ground probe to the chassis, and touch the positive probe to the tube side of the resistor so you're measuring across that 1Ohm resistor.Be sure to turn the trim pot all the way to maximum negative polarity voltage before turning anything on so the tube is running at it's coolest. You can measure this before putting the tubes in so you know you're turning the trim pot the right way.
BennJoltes
Peasant
 
Posts: 1
Joined: Wed May 25, 2016 6:11 pm

Previous

Return to Do It Yourself Amp Builders

Who is online

Users browsing this forum: No registered users and 0 guests