Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki 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

OT question  - will it work?
OT question  - will it work?
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 26th November 2008, 06:45 AM   #1
atmars is offline atmars  United States
diyAudio Member
Join Date: May 2008
Default OT question - will it work?


i got a hold of an amp chassis that had basically the same tube compliment as a 5E3 except it is a transformerless amp with 25L6s as power tubes. i also had a power transformer that would run a 5E3, so thinking myself quite clever, I set about rebuilding a deluxe into the chassis and got rid of the old tubes. Then, after reading Jack Darr I realized I probably made a big mistake. Will the OT work? Darr was talking about replacing OTs and mentioned matching load resistances and plate to plate load impedance and a realized this material is out of my depth. i can't seem to find the same kind of data on the 25l6s that are available for the 6v6s so I can't even do a side by side comparison. Can some one lend a hand here?

If I have to dump the old OT is there anything I might be able to find on ebay that will get the job done. I see a lot of pro jr. type OTs out (although i believe they run el84s) , or should I just buy a tweed deluxe replacement?

  Reply With Quote
Old 27th November 2008, 02:35 PM   #2
atmars is offline atmars  United States
diyAudio Member
Join Date: May 2008
Maybe I need to rephrase this question -

I realize that the OT will "work" but how does one calculate how it will work optimally?

What data does one use and how is it use to match on output transformer and a set of (or one) power tube?
I found this link showing how to test an unknown OT


But it does not specify how this test is done for a push pull OT.

Any insight would be greatly appreciated.
  Reply With Quote
Old 27th November 2008, 03:54 PM   #3
Tom Bavis is offline Tom Bavis
diyAudio Member
Tom Bavis's Avatar
Join Date: Jun 2002
Location: Macedon NY
The 25L6s would use a 4KCT output transformer, and 6V6s would like about 8KCT. The 6V equivalent of the 25L6 is the 6W6 - but it probably isn't worth the trouble to get a low-voltage transformer for those (and end up with half the power of 6V6s...).

You can TRY a speaker load impedance of double the original, which will present 8K to the output tubes but you'll lose an octave from the low frequency response. You may have4 to bite the bullet and get a proper 6V6 transformer.
  Reply With Quote
Old 28th November 2008, 02:25 AM   #4
atmars is offline atmars  United States
diyAudio Member
Join Date: May 2008
Thanks - I'm still waiting on parts so I will be able to do the "ear" test. If it sucks I'll try some thing else. Will a recycled blues jr. OT get the job done?
  Reply With Quote


OT question  - will it work?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Im BAAAACK! Marathon amplifier question, won't work bridged mono! 240z4u Car Audio 11 3rd April 2008 03:56 AM
Answer to the Question No One Asked-A Work in Progress.... johnbrown Analogue Source 0 7th June 2007 02:32 AM
Question on Gio's bipole sealed box - will this work? pwan Full Range 21 6th January 2007 03:48 AM
xover question; will this work? matjans Multi-Way 7 1st June 2004 01:29 PM
P3A won't work Austin Solid State 5 3rd January 2004 10:04 AM

New To Site? Need Help?

All times are GMT. The time now is 09:02 AM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio