GM70 Power supply - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 20th September 2005, 08:29 AM   #1
diyAudio Member
Join Date: Nov 2002
Location: Athens, Greece
Arrow GM70 Power supply

Good day to all. Iím planning to build a SE GM70 amplifier with self bias.

I have all the parts to build a power supply from surplus parts consist of:

One 2500V C.T. 500mA old military potted transformer
Two 2B28 Xenon tube rectifiers
One 2 uF /1500V oil capacitor
One 10mH /500mA 70 Ohm RDC choke
One capacitor bank of 100uF total

This PS gives 1290V DC with 260 mA or 1440V DC with 145mA load.
This is going to power both L and R channel
I do believe that the voltage is too high for the GM70 even if the resistor on the cathode will deduct about 80 to 100 volts (or not???).

The second option is to use two other transformers that I have in hands:

One 740V 300mA old military potted transformer
One bridge rectifier consist of one 5R4 tube and 2 silicon diodes
One 47uF cap
One One 10mH /500mA 70 Ohm RDC choke
One capacitor bank of 100uF total
This PS deliver about 940V DC @ 140mA load
In this case I will use 2 diff power supply units on for l and one for R channel.

Is there someone who builds a GM70 to help?
Any suggestions regarding the above project?
FYI the driver stage (for the moment) will be a 5842 DC coupled to a 6BG4 IT (1:1) GM70 7K OPT.
  Reply With Quote
Old 20th September 2005, 09:16 PM   #2
Fuling is offline Fuling  Sweden
diyAudio Member
Join Date: Aug 2001
Location: Sweden (Mora)
Are those chokes really 10mH?
10H seems more realistic I think.

How much experience do you have of building tube equipment?
2500V transformers and Xenon rectifiers might not be the easiest stuff to start with if you have limited experience.
  Reply With Quote
Old 21st September 2005, 08:17 AM   #3
diyAudio Member
Join Date: Nov 2002
Location: Athens, Greece
Sorry the chokes are 10H.
I have a big experience with HV due to I'm a radio amature and I have already build many KW RF power amplifiers before.

I have already build on breadboard the mentioned PS and it woks pretty good.

  Reply With Quote
Old 22nd September 2005, 01:23 PM   #4
diyAudio Member
Join Date: Mar 2004
Location: aberdeen, uk
Send a message via AIM to martinab2 Send a message via MSN to martinab2 Send a message via Yahoo to martinab2
Lots of info about GM70 applications here You need to join first but its free.
There is a data sheet here which gives a max plate voltage of 1500 for the gm70 so your first circuit would probably work nicely.
Never seen or heard xenon rectifiers in action so please let us know how it all sounds (and post some pics)
  Reply With Quote
Old 22nd September 2005, 05:49 PM   #5
amperex is offline amperex  United States
diyAudio Member
Join Date: Feb 2005
Location: MI
The 2500 volt CT transformer looks best to me. Try choke input if you need lower voltage. A power supply simulator indicates about 1100 volts DC with a choke input, MV type (3B28) rectifiers & 250 ma load. The choke input with 100uF is 'on the edge' for lower ripple. A pair of smaller current second chokes (one to each GM70) would be better even with a 2uF cap on the output.
  Reply With Quote


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
GU-50, GM70 and KT88 nina Tubes / Valves 55 19th February 2017 11:16 AM
want to do PP-GM70 day Tubes / Valves 79 10th October 2011 06:30 PM
GM70/GM70 parafeed SET? louischia Tubes / Valves 10 4th December 2008 03:12 PM
Another Gm70 amp !! HFGuy Tubes / Valves 4 8th July 2005 08:41 PM
heater supply (xformer specs are 6.3V 2.5A) as supply for a power LED? jarthel Tubes / Valves 10 21st July 2003 01:30 PM

New To Site? Need Help?

All times are GMT. The time now is 06:17 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2