UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 14th Jan 2021, 7:05 pm   #1
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Default EL34 & O/P xfmr. design notes

Intro.
In the Wanted to Buy section (q.v.) I have listed a post about my need for an O/P transformer for an EL34 valve to build a simple test rig to test a number of these valves. Since the plan is to build an item of test gear rather that an A.F. amp. as such, this thread is placed here in this particular Forum section.*

Here is a useful note (found on the www) that deals with the basics of selecting such an O/P xfmr. - and more. I found it to be informative & useful; it might be similarly useful to other members.

http://www.valvewizard.co.uk/se.html

*In my post in that WTB section there are a few posts that would be of benefit if they were moved to this thread: that will obviously be a moderator decision. This idea was inspired by a post by David (Radio Wrangler) in the appropriate thread in the WTB section, q.v.

Al.
Skywave is offline  
Old 14th Jan 2021, 8:49 pm   #2
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: EL34 & O/P xfmr. design notes

For the purposes of testing you could separate the load into its quasi-DC part, which you'd like to be very largely inductive so you don't need a very high voltage HT supply, and its AC part, which you'd like to be largely resistive.

The arrangement involves replacing the output transformer primary with a high-value choke capable of passing the DC. Apart from satisfying these two requirements it can be pretty crude. You also need to add a high-voltage capacitor from the anode, via a high power resistor, to ground. The resistance should be whatever value would have been reflected by an output transformer rom the speaker secondary into the primary. The AC part of the signal voltage will appear across this resistor.

This arrangement is sometimes used with an output transformer in place of the resistor. It makes the design of the output transformer easier since it doesn't have to handle the DC current flowing through the valve, nor does its primary have to sit at the high voltage present on the anode.

Cheers,

GJ
__________________
http://www.ampregen.com
GrimJosef is offline  
Old 14th Jan 2021, 11:06 pm   #3
Skywave
Rest in Peace
 
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
Thumbs up Re: EL34 & O/P xfmr. design notes

Thanks GJ. All of that is new to me and is worthy of further thought.

Al.
Skywave is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 7:32 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.