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 > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 10th Nov 2008, 12:11 am   #1
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Weyrad TRF Circuit

This circuit is looking very like that we have found in the constructional kits of the late forties & early fifties. There's no o/p stage, but I have got loads of 6V6's I can put to good use.
In their time these radios were known to use some very strange valves.
Here Weyrad specifically reccomend a 6K7 as RF amp and 6J7 as anode-bend detector. I suppose you could also use A EF39 and EF37A would draw less HT current, and the rectifier would be less stressed.

I was of a mind to construct the circuit. I have a chassis & case with tuning capacitors and a bagful of military surplus capacitors. There are two problems.
I don't have any guide as to setting up the RF and detector tuning so theyr'e exactly in step with each other. How were these TRF circuits of the period aligned?
The last touch for a period feel to the project would be a metal rectifier.
I am going to be awkward and see if I can get a new one. Don't expect this to be a quick build.
Attached Thumbnails
Click image for larger version

Name:	Weyrad Coils.jpg
Views:	185
Size:	85.4 KB
ID:	21159   Click image for larger version

Name:	Weyrad Diagram 1b.jpg
Views:	372
Size:	182.1 KB
ID:	21160   Click image for larger version

Name:	Weyrad Diagram 2b.jpg
Views:	182
Size:	99.0 KB
ID:	21161  
Neil Purling is offline  
Old 10th Nov 2008, 9:10 am   #2
Sean Williams
Dekatron
 
Sean Williams's Avatar
 
Join Date: Feb 2005
Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW
Posts: 3,517
Default Re: Weyrad TRF Circuit

Neil,

Look at the circuit - you will see three trimmers on each coil down to deck - these are for peaking the coils in the ant and det stages.

Cheers
Sean
__________________
Engineers make things work and have spare bits when finished
Sean Williams is offline  
Old 10th Nov 2008, 9:54 am   #3
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,550
Default Re: Weyrad TRF Circuit

Neil.

There is no 'tracking' as such in a TRF set. Usually you just peak the coils for maximum signal starting at the detector then peaking the aerial coils. Some were more elaborate than others where the reaction winding was peaked at a certain point in tuning but that doesn't look like the case here.


Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is online now  
Old 10th Nov 2008, 11:25 am   #4
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Re: Weyrad TRF Circuit

First off I would check the dial pointer was in the right place when the tuning capacitor vanes were fully open (horizontal).
I was wondering at what point in the medium wave band one should peak the trimmers.
I wondered would you do the detector first, or the aerial trimmer?
It seems like one would do the detector on a station near the low end of the band, so the station you chose was tuned n the right place on the scale.
The difficulty I see with this is to bypass the RF stage temporarily or it is a see-saw business between the two trimmers.
Neil Purling is offline  
Old 10th Nov 2008, 8:18 pm   #5
Variometer
Retired Dormant Member
 
Join Date: May 2008
Location: Preston, Lancashire, UK.
Posts: 428
Default Re: Weyrad TRF Circuit

I have never found it all that critical. With two valves, trimming would probably increase the volume a bit, but still ample without. If you don't want to bother trying to find the "genuine" Weyard cails, just use RF chokes, they work just as well. For MW, I use 200uH (two 100uH in series if you can't find a 200uH choke). Saves a lot of messing about & they are very inexpensive.
Bob
Variometer is offline  
Old 11th Nov 2008, 2:18 pm   #6
Neil Breward
Retired Dormant Member
 
Neil Breward's Avatar
 
Join Date: Aug 2005
Location: Keyworth nr. Nottingham, UK
Posts: 140
Default Re: Weyrad TRF Circuit

Quote:
Originally Posted by Richard_Newman View Post
Neil.

There is no 'tracking' as such in a TRF set. Usually you just peak the coils for maximum signal starting at the detector then peaking the aerial coils. Some were more elaborate than others where the reaction winding was peaked at a certain point in tuning but that doesn't look like the case here.


Rich.
Some 1930's TRFs, eg Cossors, actually brought an aerial trimmer knob out front to tweak the alignment of the tuned circuits for optimum reception.

Cheers,
Neil
Neil Breward is offline  
Old 11th Nov 2008, 8:32 pm   #7
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Re: Weyrad TRF Circuit

This circuit is about as simple as they come.
Old issues of PW show that people like Premier used some odd valves at times live a CV1510 (B9G base) and a ATP4 (Mazda Octal). They did revert to using a normal 6V6 in their AC only TRF's. It seems that the obscure output valves pulled more anode & screen current, so i'll keep with a EL32 or a 6V6. I dunno what the average o/p power would be for a EL32 & 6V6 in single ended use.
Neil Purling is offline  
Old 11th Nov 2008, 8:52 pm   #8
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,550
Default Re: Weyrad TRF Circuit

Quote:
Originally Posted by Neil Purling View Post
This circuit is about as simple as they come.
Old issues of PW show that people like Premier used some odd valves at times liKe a CV1510 (B9G base) .
This is actually a small transmitting valve similar to the Mullard QV04-7. The National Valve Museum show it used in a small RF PA circuit.

I had one of these TRF's in the 60's. Unfortunately it didn't survive my curiosity when a capacitor failed!


Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is online now  
Old 12th Nov 2008, 10:48 pm   #9
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Re: Weyrad TRF Circuit

I used the National Valve Museum data to work out the anode & screen current for the valves that the 3 valve TRF's might use and the necessary rating for a rectifier stack.
Those transmitter valves are obviously would do a reasonable job. I am curious about them but not enough to install one because I have a lot of 6V6's and a pair of VT52 (EL32) for the audio stage. I may sell the EL32's. The 6V6 is more powerful, but is biased very conservatively. The Repanco diagram left it to the builder to choose a AF o/p stage of their own.
I am taking this kit radio right down to the bare chassis. It is going to be a single band 3 valve TRF, hopefully looking as much like a amateur project radio of yesteryear as is possible.
This would mean a metal rectifier stack of course. It will happen if I ever hear from Cougar Electronics again. I have got a bunch of old Federal 1004A's. I will try one pair and see if they are fit to use. I would not leave the radio unattended, but I don't use it heavily.
Neil Purling is offline  
Old 17th Nov 2008, 11:00 pm   #10
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Re: Weyrad TRF Circuit

I have seen a listing of the Federal 1004A in what I assume is a advert of the product range. Trouble is, I don't know what'd be the sort of fwd & reverse resistances to expect in a good one and how much drift puts the thing in danger of getting all hot, & stinky.
The requirement is to rectify 250V, so that means a pair of the Federal 1004A or Brimar RM3.
Hmm..... Can I tell if a NOS rectifier has aged badly from a check with my AVO 8?
Neil Purling is offline  
Old 19th Dec 2008, 9:10 pm   #11
Neil Purling
Nonode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 2,083
Default Re: Weyrad TRF Circuit

This TRF did not have a 'good sound' before the rebuild and it didn't after, which I attributed to the anode bend detector. I put a 0.047uf @ 600V capacitor between the 6V6 anode pin and chassis. It gives a much more mellow result without sounding muffled.
Neil Purling is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 10:31 am.


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.