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.

Closed Thread
 
Thread Tools
Old 12th Dec 2017, 10:17 pm   #61
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by Michael Maurice View Post
The Vishay ones are rated at 500V, use them. When the amplifier is completed and working, no-one will see whats inside, so does it really matter!
Thanks Michael, actually they are all rated at 500V!

Quote:
Originally Posted by HamishBoxer View Post
As long as they are fitted neatly and correct rating,then that really is all that matters.
Agreed just for myself i want to know whats in there, i want it neat and all similar.
vishalk is offline  
Old 14th Dec 2017, 6:59 pm   #62
rtbcomp
Tetrode
 
rtbcomp's Avatar
 
Join Date: Aug 2007
Location: Sheffield, South Yorkshire, UK.
Posts: 50
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by greg_simons View Post
excellent idea replacing the fuse resistor with a real glass fuse, I have no idea why they never fitted one in the first place although the cost of a bulgin fuse holder and glass fuse was way more expensive than a simple resistor...
I suspect it may have something to with surges, the resistor melting the solder will break the circuit under high average current, whereas a fuse will fail on a current spike.

I don't know if anti-surge fuses were available when these amps were new, but maybe if you do fit a fuse then choose an anti-surge type??
rtbcomp is offline  
Old 14th Dec 2017, 8:22 pm   #63
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by greg_simons View Post
... excellent idea replacing the fuse resistor with a real glass fuse, I have no idea why they never fitted one in the first place ...
No, rather bad idea in fact. The 100ohm resistor is not there mainly as a fuse. It's there mainly to separate the reservoir capacitor from the first smoothing capacitor. It serves a real electronic purpose. You can add a fuse as well if you want.

A few years ago there was a thread here somewhere where Stephen Spicer and I discussed the use of this resistor as a protection device. I and others have seen Stereo20s where the tags on the board are not cut, so in the event of the solder melting the resistor wouldn't drop out. My best guess is that actually Leak found that it didn't offer much protection in practice so they simply stopped bothering to cut the tags.

The reason Leak didn't fit a fuse would have been some combination of cost (he was running a business and very few of his competitors were paying for an HT fuse) and practicality. The output transformer primary windings are a bit marginal. So a protective fuse would have had to have been rated at a current quite close to the normal operating level . That would have resulted in some degree of 'nuisance blowing' which would have upset the customers.

As far as the look of the resistors goes, we shouldn't forget that Leak didn't pay for a baseplate for this amp either. So we can see the resistors whenever we lift the amp and look. Leak set a lot of store by appearance (it was a selling point that they were proud of). So in much the same way that while your E-type will drive just as well on solid wheels, you really want it to have the lovely looking wire ones don't you ?

VB
__________________
http://www.ampregen.com
GrimJosef is online now  
Old 14th Dec 2017, 9:07 pm   #64
frankmcvey
Rest in Peace
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 858
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
I and others have seen Stereo20s where the tags on the board are not cut, so in the event of the solder melting the resistor wouldn't drop out.
Of the two ST20s I restored earlier this year, one had R21's tags cut, the second didn't. I modified the second one on the presumption that some protection is better than none.

During the soak check afterwards, one of the amps cut out, because it had overheated and R21 had dropped out. The reason, I suspect, was that up to that time I had been running the amps on their sides so that I could monitor voltages etc. During the soak check I had this amp standing on its base - there were no feet fitted, so there was no circulation of air under the amp contributing, I suspect, to the build up of enough heat to desolder the resistor. After refitting it and fitting feet, it was fine.

Cheers,

Frank
frankmcvey is offline  
Old 14th Dec 2017, 11:09 pm   #65
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

It took most me of the day, but I was able to finish fitting the components today, keeping what was in range and replace where it was needed.

I found the input/preamp area fiddly and a real pain especially since the resistors were hooked around the terminals and so close together.

I didn't have small 32uf caps for the power supply, so just to get it tested I used the black replacements as you see, I carefully took the original ones out to change back at a later stage.

Once everything was double checked, it was switched on without any valves and transformer voltages checked again.

Then one by one each valve, starting with the rectifier, was inserted and the voltages and current drawn was checked around the circuit.

So far everything is as it should be! Next will be to actually put some test tones through it and check it all on the oscilloscope, do a soak test, play some music through it and make sure it runs sweetly.

Any tips here would be appreciated, Once I get to that stage I'll start tidying it all up. So far very happy.
Attached Thumbnails
Click image for larger version

Name:	IMG_20171214_175849.jpg
Views:	418
Size:	102.3 KB
ID:	153995   Click image for larger version

Name:	IMG_20171214_180529.jpg
Views:	178
Size:	94.5 KB
ID:	153996  
vishalk is offline  
Old 14th Dec 2017, 11:21 pm   #66
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by frankmcvey View Post
Quote:
I and others have seen Stereo20s where the tags on the board are not cut, so in the event of the solder melting the resistor wouldn't drop out.
Of the two ST20s I restored earlier this year, one had R21's tags cut, the second didn't. I modified the second one on the presumption that some protection is better than none.

During the soak check afterwards, one of the amps cut out, because it had overheated and R21 had dropped out. The reason, I suspect, was that up to that time I had been running the amps on their sides so that I could monitor voltages etc. During the soak check I had this amp standing on its base - there were no feet fitted, so there was no circulation of air under the amp contributing, I suspect, to the build up of enough heat to desolder the resistor. After refitting it and fitting feet, it was fine.
Great Tip Frank, i was thinking of getting some sheet perspex, cutting it to size and using a drill press to cut some holes for ventilation and propping it up on some feet.
vishalk is offline  
Old 14th Dec 2017, 11:23 pm   #67
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
Originally Posted by GrimJosef View Post
Quote:
Originally Posted by greg_simons View Post
... excellent idea replacing the fuse resistor with a real glass fuse, I have no idea why they never fitted one in the first place ...
No, rather bad idea in fact. The 100ohm resistor is not there mainly as a fuse. It's there mainly to separate the reservoir capacitor from the first smoothing capacitor. It serves a real electronic purpose. You can add a fuse as well if you want.
Yes this was discussed about this resistor and its importance, a fuse will be added after that resistor.

Quote:
A few years ago there was a thread here somewhere where Stephen Spicer and I discussed the use of this resistor as a protection device. I and others have seen Stereo20s where the tags on the board are not cut, so in the event of the solder melting the resistor wouldn't drop out. My best guess is that actually Leak found that it didn't offer much protection in practice so they simply stopped bothering to cut the tags.

The reason Leak didn't fit a fuse would have been some combination of cost (he was running a business and very few of his competitors were paying for an HT fuse) and practicality. The output transformer primary windings are a bit marginal. So a protective fuse would have had to have been rated at a current quite close to the normal operating level . That would have resulted in some degree of 'nuisance blowing' which would have upset the customers.

As far as the look of the resistors goes, we shouldn't forget that Leak didn't pay for a baseplate for this amp either. So we can see the resistors whenever we lift the amp and look. Leak set a lot of store by appearance (it was a selling point that they were proud of). So in much the same way that while your E-type will drive just as well on solid wheels, you really want it to have the lovely looking wire ones don't you ?
I want wire wheels!
vishalk is offline  
Old 15th Dec 2017, 12:08 am   #68
frankmcvey
Rest in Peace
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 858
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Quote:
i was thinking of getting some sheet perspex, cutting it to size and using a drill press to cut some holes for ventilation and propping it up on some feet.
Well, as GJ says, the original came without any base at all, although you could buy after-market bases. The amps were designed to be fitted in a cabinet and hidden from view and questing little fingers. Something you'll have to think about in a year or two's time when your bairn becomes a toddler!

I've probably got some smallish rubber feet I can let you have.

Cheers,

Frank
frankmcvey is offline  
Old 15th Dec 2017, 3:40 pm   #69
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Post man came today with some more gifts.

Russian PIO capacitors and a full component kit to repair the TL12 plus, thanks to Paul at Classic Sounds Leicester.
Attached Thumbnails
Click image for larger version

Name:	IMG_20171215_143037.jpg
Views:	141
Size:	123.5 KB
ID:	154024   Click image for larger version

Name:	IMG_20171215_143055.jpg
Views:	127
Size:	68.4 KB
ID:	154025   Click image for larger version

Name:	IMG_20171215_143105.jpg
Views:	124
Size:	70.4 KB
ID:	154026   Click image for larger version

Name:	IMG_20171215_143459.jpg
Views:	113
Size:	82.2 KB
ID:	154027  
vishalk is offline  
Old 16th Dec 2017, 12:22 am   #70
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Thought i would do a parts list for the TL12 plus. Taken from the circuit diagram supplied in Stephen Spicer's book.

only thing which was confusing was C13 (smoothing cap) it has at 200uf, so far i've seen three different circuit diagrams with different values for C13 - 32uf,100uf and 200uf.
C14 - 32uf, 60uf,8uf

Like seriously which one is it? I downloaded circuit diagrams from well known websites and each one is different.

Unfortunately my original caps are finished and need changing so not sure which i should use. Thinking stick the the Stephen Spicer Diagram C13 being 200uf and C14 8uf

Please have a look and let me know if i made any mistakes! Trying to provide help for other future enthusiasts.

LEAK TL12 PLUS
Resistors
Qty Designator Original Value
R1 1M, 1/2W
R2 22K,1/2W
R3 2K2, 1/2W
R4 100R, 1/2W
R5 82K 1/2W
R6 1M ,1/2W
R7 100K, 1W
R8 3.3M
R9 91K
R10 1K
R11 22K,1/2W
R12 12K or 1M ,1/2W
R13 100K, 1W
R14 3.3M
R15 10K, 1/2W
R16 470k
R17 470k
R18 10K, 1/2W
R19 270K
R20 270K
R21 10K
R22 100R, 3W
R23 4.7K

Capacitors
Qty Designator Original Value
C1 1000pf
C2 50uF electrolytic,12v
C3 1uf 450v
C4 0.1uf 350v
C5 16uf
C6 8uf
C7 200pf
C8 0.025uf 350v
C9 0.1 uf 450v
C10 0.025uf 350v
C11 50uf
C12 50uf 12v
C13 200uf
C14 60 uf
C15 200pf

Last edited by vishalk; 16th Dec 2017 at 12:30 am.
vishalk is offline  
Old 16th Dec 2017, 10:23 am   #71
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Your list has redundant "Qty" headings in it!
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 16th Dec 2017, 12:05 pm   #72
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Did it late last night, eyes were tired so missed it when I copied and pasted it!

Either way the list is there, I'll correct and repost.
vishalk is offline  
Old 17th Dec 2017, 11:03 pm   #73
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

One off topic post deleted.
AC/HL is offline  
Old 18th Dec 2017, 10:54 pm   #74
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

As I write this the stereo 20 is in the background playing Michael Buble Christmas songs (wife's choice of music)

Its been playing for 4 hours with no issues and I must say it's a joy to listen to. Beautiful warmth to it and not fatiguing to listen to.

I'm running through a valve preamp with no issues at all, so I have no problem with the input gain.

Using the function generator and oscilloscope I managed to get 10wrms per channel, everything was as it should be!

Next is the pair of TL12 + although these will have a few slight modifications.
Attached Thumbnails
Click image for larger version

Name:	IMG_20171218_114818.jpg
Views:	142
Size:	73.8 KB
ID:	154190   Click image for larger version

Name:	IMG_20171218_114824.jpg
Views:	128
Size:	73.0 KB
ID:	154191   Click image for larger version

Name:	IMG_20171218_114829.jpg
Views:	145
Size:	62.0 KB
ID:	154192   Click image for larger version

Name:	IMG_20171218_205033.jpg
Views:	133
Size:	69.8 KB
ID:	154193   Click image for larger version

Name:	IMG_20171218_205118.jpg
Views:	143
Size:	53.9 KB
ID:	154194  

vishalk is offline  
Old 18th Dec 2017, 11:23 pm   #75
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Guys do any of you have some spare leak power bulgin connectors i can purchase, please PM me if you do!

Thanks
vishalk is offline  
Old 18th Dec 2017, 11:28 pm   #76
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default A pair of Leak TL12s

To avoid confusion, please start a new thread for the TL12s
AC/HL is offline  
Old 26th Dec 2017, 8:54 pm   #77
vishalk
Pentode
 
Join Date: Aug 2017
Location: North London, UK.
Posts: 114
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Hi All

I hope you are enjoying the Xmas festivities, for me it started off with my leak amplifier dying on me.

My wife on Xmas day switched the system on, although didn't wait for the amplifier to warm up before playing music. She tells me one of the EL84 valves flashed and glowed brightly, at which point she saw smoke and smelt burning! This is where she switched it all off (I was in the shower when all this happened).

Please see attached pictures, resistor R15 burnt out taking the associated EL84 valve with it.

Now I'm not sure why as it's been working beautifully, upset as it took out one of the quad matched Mullards .

Could it be that the valve just became faulty? Or is it one of the components?

Means I have to recheck all the component values and retest the voltages.

Anything else I should look out for?
Attached Thumbnails
Click image for larger version

Name:	IMG-20171225-WA0012.jpg
Views:	148
Size:	64.5 KB
ID:	154463   Click image for larger version

Name:	IMG-20171225-WA0014.jpg
Views:	141
Size:	56.3 KB
ID:	154464  
vishalk is offline  
Old 26th Dec 2017, 10:41 pm   #78
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

OK, replace the resistor (obviously) and then check that no DC can be measured on the grid of the burnt out valve. Do this with no output valves plugged in or even with no valves except GZ34, this will eliminate a leaky coupling capacitor which could cause the valve to pass more current than its rated for and cause it to fail. Make sure no short circuits anywhere. then check all the voltages at the various key points with a set of known good valves in. I am assuming that you did replace all the coupling caps with new plastic film jobs of a suitably high DC voltage rating?
As I remember you are using the Mullards that the amp came with? It's quite possible that it simply died of old age and unfortunately failed in a manner that took out the cathode resistor.
I'd put the other 3 Mullards to one side once sure the amps ok and replace the lot with decent new ones. And flog the other 3 on Ebay, you'll likely cover the cost of a new quad of Russian or Chinese etc etc that way.

A.

Last edited by bikerhifinut; 26th Dec 2017 at 10:45 pm. Reason: clarification
bikerhifinut is offline  
Old 26th Dec 2017, 11:13 pm   #79
frankmcvey
Rest in Peace
 
Join Date: Jan 2015
Location: Cottesmore, East Midlands, UK.
Posts: 858
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Hi, Vishal,

I had exactly the same problem on one of the ST20s I did back in March or so. All the surrounding components checked in spec and the voltages looked good. In the end I decided that the resistor was was simply not man eneough for it's supposed wattage and replaced all 4 main cathode resistors with higher wattage items (IIRC 3W) When I fitted the new ones, I stood them away from the board by about 6-8 mm or so to allow better circulation.

If all else looks good, you might try that. And remember that you can't have the amp sitting right down on to its chassis - you need some sort of feet to raise it enough to allow cool air to get in under the chassis.

Cheers,

Frank

Last edited by frankmcvey; 26th Dec 2017 at 11:19 pm.
frankmcvey is offline  
Old 26th Dec 2017, 11:30 pm   #80
bikerhifinut
Octode
 
Join Date: Nov 2013
Location: Penrith, Cumbria, UK
Posts: 1,993
Default Re: Leak Stereo 20 and TL12 Plus in need of recommissioning. Help and Guidance needed

Well spotted Frank. Yes I'd replace all 4 270R cathode resistors and as frank says, stand them off to let air get round. 2W should be well man enough though. I used the bog standard 2W metal films from uncle Maplin and they are still there some 13 years later! They will be dissipating around 0.6W so 2W should be plenty of headroom. Those 2W Maplin jobs are a similar size to the originals which I think might have only been 1W jobs all those years ago.

Otherwise totally in agreement with you frank

Andy.
bikerhifinut is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:09 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.