funky power supply - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th March 2008, 11:01 PM   #1
diyAudio Member
 
Join Date: Oct 2006
Location: Los Angeles
Default funky power supply

I picked up an EL34 PP amp from a garage sale that I am now going to restore. The power supply looks pretty interesting and I was wondering if I could safely remove the 75u cap from the circuit?

I mapped out the circuit and the power supply indeed looks like that...
Attached Images
File Type: jpg psu.jpg (12.5 KB, 352 views)
  Reply With Quote
Old 18th March 2008, 11:02 PM   #2
diyAudio Member
 
Join Date: Oct 2006
Location: Los Angeles
PS: The first two 50u caps are not polarized!
  Reply With Quote
Old 18th March 2008, 11:26 PM   #3
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
That circuit cannot possibly work like that. You can't put a diode across a 70 volt winding with only a ten ohm resistor. Makes no sense. Check it again.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 19th March 2008, 01:21 AM   #4
diyAudio Member
 
Join Date: Oct 2006
Location: Los Angeles
Hey HollowState, I'm pretty sure that's how its connected. There are four red leads from the power transformer. One is grounded. The other supplies 7.5V The third one is connected to the 10R resistor and it measures 140Vpk to ground. The fourth red lead is connected to the 75u cap which also measured 140Vpk. These two points are finally connected to a dual section planet cap. The other leads on the power transformer is the heater grn-grn/yel-grn leads so I assume that the two red leads are the HT. Also the diode going to ground has a 1F snummber cap.

I'm pretty confused myself about how this works; the amp plays music and the only problem is that it is quite noisy (mostly 60Hz hum). I double checked all the wiring again to be sure as I'm definitely no expert I yanked out the transformers today to mark out the new chassis bit I'll post a pic of the chassis soon. Thanks.
  Reply With Quote
Old 19th March 2008, 01:44 AM   #5
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
Well, all I know is what I see in your drawing, which can't work as shown. If your transformer (secondary?) has four red leads, you're only showing three.
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote
Old 19th March 2008, 02:00 AM   #6
diyAudio Member
 
Join Date: Oct 2006
Location: Los Angeles
So heres a pic of the PSU section.

1. One red lead from the power transformer was connected to A, a 70u cap. A was connected to C via a dual section 50u+50u cap. I measured A at 140V.
2. The other red lead was connected to B, to 10W power resistors measuring 10 ohms. At B was also at 140V.
3. The power resistors are connected to C through a diode. C measured 280V.
4. From C we have 2 130R resistors connected to reservoir caps that connect to the EL34 plates.
5. Also note the diode that goes from the power resistors to ground (chassis!).
Attached Images
File Type: jpg psu.jpg (83.7 KB, 234 views)
  Reply With Quote
Old 19th March 2008, 02:03 AM   #7
diyAudio Member
 
Join Date: Oct 2006
Location: Los Angeles
The 4th red lead that measured 7V was connected to a couple of tube socket heaters that formed the radio receiver. The second heater pin on all these sockets were connected to ground at the chassis. Also, shouldn't this red lead also have a 0V lead? Or is the CT lead the reference for this 7V lead as well? The main amp circuit (EL84's and 12AU7) had heater supplied via two green leads which also had a CT connected at one of the EL34 cathodes.

There are so many chassis grounds its amazing. Whats worse, the amp power plug is only two pin

Thank you for being patient, HollowState.
  Reply With Quote
Old 19th March 2008, 02:35 AM   #8
cerrem is offline cerrem  United States
diyAudio Member
 
Join Date: Jun 2005
Location: San Diego, CA
The 130 ohm resistors are completely rediculous....
It was a way of trying to reduce capacitor in-ruch currents from poping the diodes or such...but they add to the caps ESR and put a nasty ZERO in the response....
The ZERO is obviously above the 120Hz ripple, but have an adverse affect on the higher frequency audio signal currents that these caps are suppose to bypass to ground and back to the cathodes of the output stage...
I would remove those 130 ohm resisitors and make sure to use diodes that can handle the start-up surge current...

Chris
  Reply With Quote
Old 19th March 2008, 02:56 AM   #9
diyAudio Member
 
Join Date: Oct 2006
Location: Los Angeles
Yes, I will definitely use some sturdier hexfred diodes. Also all grounds are on chassis including the psu grounds and the CT too. The socket lugs and the extra pins on the input selector were used as high voltage nodes to distribute plate voltages throughout the chassis. One such hv node also happens to be on TOP of the chassis connected to one of the radio tuner knobs. This point was exposed probably because the knob cover was destroyed over time. I hope this amp dint fry any of its previous owners
  Reply With Quote
Old 19th March 2008, 03:12 AM   #10
diyAudio Member
 
HollowState's Avatar
 
Join Date: Aug 2006
Location: Taxland, New Jersey
As I suspected earlier, you have a standard voltage doubler that was drawn incorrectly. I think it looks like the crude hand sketched one below.

Victor
Attached Images
File Type: jpg mvc-009s.jpg (37.3 KB, 213 views)
__________________
"It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong." ~Thomas Sowell
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Funky Looking 15DQ8s wrenchone Tubes / Valves 14 29th March 2009 08:21 PM
Class D amp, one channel ... funky. guitarcarl Class D 1 20th November 2008 08:57 PM
Funky 70's SAE preamp and amp (ebay) Jason Swap Meet 0 8th April 2005 11:51 AM
funky T-S values; drivers any use?!? sean99 Multi-Way 5 14th August 2004 07:02 PM


New To Site? Need Help?

All times are GMT. The time now is 07:00 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2