Zenith OPT question - 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 14th July 2010, 04:00 PM   #1
no gas is offline no gas  United States
diyAudio Member
 
Join Date: Jul 2010
Location: Los Angeles
Default Zenith OPT question

I've got an old Zenith PP OPT that has an uneven primary. One half measures 56 ohms less than the other and in the original amp there was a 56 ohm resistor on that side. My question is, how do I use this OPT? Can I drive it with the normal phase splitter? Thanks for any guidance.
  Reply With Quote
Old 14th July 2010, 05:01 PM   #2
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
I'd probably start with something else were it me, however if you use it in a manner analogous to the original design with any phase splitter you choose (if I understand you correctly) it should not be an issue. Just how good that OPT actually is might be an issue however.
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 14th July 2010, 08:24 PM   #3
no gas is offline no gas  United States
diyAudio Member
 
Join Date: Jul 2010
Location: Los Angeles
It's a fairly heafty 15w or so out of a 7K31 series Zenith. Next question is why it would be uneven?
  Reply With Quote
Old 14th July 2010, 08:57 PM   #4
diyAudio Member
 
richwalters's Avatar
 
Join Date: Sep 2003
Location: Alps:Tube amp designs over 150W, SMPS guru.
Primaries not wound equally on core. One half prim innermost to core has lower resistance and other half prim wound outer equals higher resistance due to longer MLT.(mean length per turn) and secs plonked somewhere in the middle. A mass produced NON quality product, but it works.
For use in a cathode bias o/p stages, the unsymmetrical problem is solved automatically and this is where it was intended.

richy
  Reply With Quote
Old 14th July 2010, 09:23 PM   #5
no gas is offline no gas  United States
diyAudio Member
 
Join Date: Jul 2010
Location: Los Angeles
Thank you for a concise answer. Makes sense to me. Well, at least the power transformer is a beast!
  Reply With Quote
Old 14th July 2010, 10:54 PM   #6
20to20 is offline 20to20  United States
diyAudio Member
 
20to20's Avatar
 
Join Date: Jun 2010
Location: W-S, NC
Zenith seems to be one oddball engineering company. I have a 7D30 chassis that takes the 8 ohm Channel 1 output and doesn't send it to a speaker. They send the line back over to Channel 2 OPT and run it right into a centertap of the secondary 16 ohm coil, and then use 2 taps on that OPT for output to the speakers. AND never mind the additional secondary coils on each OPT of @50 ohms for a dedicated feedback circuit, not tapped off of the speaker terminal like 90% of other amps.

You ought to get the PDF diagram from Sams and see what's what. You might find you have a couple of trannys with a special design.
  Reply With Quote
Old 15th July 2010, 12:48 AM   #7
diyAudio Member
 
tubelab.com's Avatar
 
Join Date: Jul 2005
Location: West Virginia panhandle
Quote:
I've got an old Zenith PP OPT that has an uneven primary. One half measures 56 ohms less than the other and in the original amp there was a 56 ohm resistor on that side.
That is pretty common in cheap OPT's. I have a big bunch of bottom dollar P-P OPT's designed for guitar amps. There is no interleaving whatsoever. One half-primary is wound first, then the entire secondary, then the other half-primary. Both half-primaries have the same number of turns but the outer one has a larger diameter, so it has more resistance, even though in my case it is wound with a thicker wire.

I use them in the same manner as any other OPT, the resistor is probably not necessary. I have found that in fixed bias amps the lowest distortion is often achieved with slightly unequal tube currents. I find the same thing with high dollar Plitrons though.
__________________
Too much power is almost enough! Turn it up till it explodes - then back up just a little.
  Reply With Quote
Old 15th July 2010, 01:02 AM   #8
diyAudio Member
 
Join Date: Nov 2007
Location: Dallas
Is one of those weirdos that send A+B through bass transformer, and A-B
through the smaller cheaper one that would saturate at low frequency?

I'm asking, not sayin'... I've never actually seen real one like that (yet).

Hmmm... Suddenly thinking new abuse for toroid here.

Last edited by kenpeter; 15th July 2010 at 01:07 AM.
  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
OPT question Andrewbee Tubes / Valves 3 11th May 2009 11:35 PM
Zenith Console Opt Question, Odd Secondary Trout Tubes / Valves 10 3rd October 2005 02:20 AM
opt question skyraider Tubes / Valves 6 23rd June 2005 06:36 AM
What can I do with these? (tube and OPT question) needtubes Tubes / Valves 7 8th March 2005 01:01 PM
Question on OPT MlinarS Tubes / Valves 2 26th February 2005 12:55 PM


New To Site? Need Help?

All times are GMT. The time now is 06:30 PM.


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