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 Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Reply
 
Thread Tools
Old 17th Jun 2021, 8:10 pm   #21
wd40addict
Octode
 
wd40addict's Avatar
 
Join Date: May 2009
Location: Stevenage, Herts. UK.
Posts: 1,019
Default Re: Quad II Transformer woes!

I once tried an RS 100V line transformer together with a loan Vortexion 50W 807 PA amp into my Hi-Fi speakers. I expected it to just 'work', but it actually sounded amazingly good!
wd40addict is offline   Reply With Quote
Old 18th Jun 2021, 3:26 pm   #22
Vintage Engr
Hexode
 
Join Date: Jan 2008
Location: Shrewsbury, Shropshire, UK.
Posts: 294
Default Re: Quad II Transformer woes!

Interesting to hear about the output transformer problems.
I have a Quad II which I 'rescued' from a company that went under. The Quad is actually new, & appears not to have been used, & still in its original but tatty box.
I've had it for around 40 years, & checked it out a few months ago. Unbelievably, the output transformer is o/c on one of the secondary windings!
I'm wondering if perhaps the wire was never soldered to its relevant tag.
But how did it pass a final test?

I'm hoping to sneak the transformer past my wife into a warm oven at some point so that I can disassemble it.

Incidentally Canford Audio used to do an HQ 100v line 'Music' transformer, which I have installed where I needed better quality speakers, & the results were very good.

David.
Vintage Engr is offline   Reply With Quote
Old 18th Jun 2021, 3:36 pm   #23
Petedox
Pentode
 
Petedox's Avatar
 
Join Date: Feb 2020
Location: Waterlooville, Hampshire, UK.
Posts: 139
Default Re: Quad II Transformer woes!

Thanks for info David, I've just looked at their site and the HQ transformers look very affordable.
__________________
Pete
Petedox is online now   Reply With Quote
Old 18th Jun 2021, 6:15 pm   #24
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 6,834
Default Re: Quad II Transformer woes!

Hi Gents, it should be quite easy to wind a good quality 100v line matching transformer that would be of a similar size to, and used with the Quad. It could also be wound using an interleaving method. Given the presence of an additional transformer in the chain I would expect a marginal increase of distortion.

On a theoretical front, as isolation is no longer required, the transformer coul be an autowound type and more compact.

Only a few thoughts, please discuss

Ed
Ed_Dinning is online now   Reply With Quote
Old 18th Jun 2021, 6:25 pm   #25
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 3,608
Default Re: Quad II Transformer woes!

Quote:
Originally Posted by Vintage Engr View Post
... Unbelievably, the output transformer is o/c on one of the secondary windings!
I'm wondering if perhaps the wire was never soldered to its relevant tag.
But how did it pass a final test? ...
Sorry if this is teaching my granny to suck eggs, but are you certain ? The secondary turrets on the 'normal' i.e. 8ohm/15ohm transformer are P, Q, R, S, and T. But there are actually two completely separate windings - one goes between P and S with Q as a tapping, the other goes between R and T. So if you try to measure each 'section' from P all the way to T you'll find a break between R and S. This is how it's meant to be. PQ is the negative feedback section. For 8ohm speakers QS and RT have to be connected, with jumper wires, in parallel. For 15ohm ones they have to be connected, with one jumper, in series.

Cheers,

GJ
__________________
http://www.ampregen.com

Last edited by GrimJosef; 18th Jun 2021 at 6:34 pm.
GrimJosef is offline   Reply With Quote
Old 18th Jun 2021, 9:02 pm   #26
Vintage Engr
Hexode
 
Join Date: Jan 2008
Location: Shrewsbury, Shropshire, UK.
Posts: 294
Default Re: Quad II Transformer woes!

I am aware of the connections on this particular transformer, I had hoped that someone had simply miss-wired it, but not so!

I will take it apart some time, but unfortunately have more pressing issues at present.

David.
Vintage Engr is offline   Reply With Quote
Old 18th Jun 2021, 10:33 pm   #27
Chris55000
Octode
 
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 1,712
Default Re: Quad II Transformer woes!

Hi!

Quote:
Available as a free pdf download from http://www.tubebooks.org/Books/Atwoo...t%20Design.pdf
That pdf linked has nothing in common with "High Fidelity Sound Engineering" the book I referred to is written in British terminology and is far more theoretical in content than the pdf quoted!

Chris Williams
__________________
It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!
Chris55000 is offline   Reply With Quote
Old 19th Jun 2021, 9:39 pm   #28
Cobaltblue
Moderator
 
Cobaltblue's Avatar
 
Join Date: Dec 2010
Location: Exeter, Devon and Poole, Dorset UK.
Posts: 4,985
Default Re: Quad II Transformer woes!

Some interesting posts that were a wee bit off topic have been moved here.

https://www.vintage-radio.net/forum/....php?p=1382776

Cheers

Mike T
__________________
Don't care if it was a bargain why's it in my kitchen
Mike T BVWS member.
www.cossor.co.uk
Cobaltblue is offline   Reply With Quote
Old 20th Jun 2021, 2:09 am   #29
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 539
Default Re: Quad II Transformer woes!

Quote:
Originally Posted by murphymad View Post
There is the hidden resistor which is made up from a couple of loops of winding wire in a specific place.
Mike...
Mike can you indicate where the 'hidden resistor' is located in the various winding sections? Given it is made from 'loops' of winding wire then that suggests it may be acting in a way as to balance primary half-winding leakage inductances (if located in a primary winding section), or even possibly a small inductance in the feedback secondary winding that carries secondary current and acts as a way to add some phase advance at very high frequency for stability.

BTW, the 1961 Crowhurst book "High Fidelity Sound Engineering" is available on-line (just google search for it) and interesting to note how Crowhurst has summarised the preceding decade of knowledge on certain matters.
trobbins is offline   Reply With Quote
Old 20th Jun 2021, 7:01 pm   #30
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 6,834
Default Re: Quad II Transformer woes!

Hi Tim, from memory this part was a few turns of winding wire (10?) in a strip of SRBP and was perhaps 6mm in dia.
I believe it was connected between 2 winding sections and was just buried in the pitch

Ed
Ed_Dinning is online now   Reply With Quote
Old 20th Jun 2021, 7:14 pm   #31
Petedox
Pentode
 
Petedox's Avatar
 
Join Date: Feb 2020
Location: Waterlooville, Hampshire, UK.
Posts: 139
Default Re: Quad II Transformer woes!

If you scroll down almost to the bottom of this link, you can see Keith Snooks interpretation of the transformer windings including the resistor.

http://www.keith-snook.info/quad-ii-...amplifier.html
__________________
Pete
Petedox is online now   Reply With Quote
Old 21st Jun 2021, 1:58 am   #32
trobbins
Heptode
 
trobbins's Avatar
 
Join Date: Oct 2009
Location: Melbourne Australia
Posts: 539
Default Re: Quad II Transformer woes!

Thanks. So the extra resistor 'loop' is in series with the innermost wound section of the feedback winding (P-Q). It's plausible that the additional resistance or leakage inductance (or both) provided by that 'loop' is balancing some high frequency characteristic.

It does seem a bit strange that the stated resistance of the resistor 'loop' is 0.36 ohm and the stated resistance of P-Q is the same as Q-S at about 0.55-0.61 ohm, and that each secondary winding section that comprises P-Q and Q-S are each comprised of 51 turns. Given the photo of the resistor 'loop' showing only a few turns on a small SRBP strip, I'd expect it to be a lot less than 0.36 ohm given that the wound sections total up to be 0.55-0.61 ohm. Maybe 0.36 ohm relates to the total L2 winding section that contributes to P-Q, and not just the resistor 'loop' itself. As such, it seems that the resistor 'loop' is more about its leakage inductance contribution than its resistance contribution.
trobbins is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 8:33 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 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.