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 24th Oct 2010, 1:40 pm   #121
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

They are (I think more modest) 150s and came with the amp which I bought in a rush just before I came over here. One of the best things I have ever bought as far as value for money and pleasure given goes. They are great speakers and sound terrific IMO but I am wondering if I should change the crossover caps. Thanks to some advice from Radio_Dog I was able to have a look at them today and I will go ahead and change them as soon as I can source the parts here or I need to order more bits from the UK anyway. The £7 delivery change is hard to swallow for 4 caps that cost £1.20.
Wage Slave is offline  
Old 25th Oct 2010, 4:53 am   #122
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

The symptoms I described earlier are definitely correct. The only thing I didn't mention is that tuner 1 is a more sensitive input than tuner 2. That is logical as there are resistors on Tuner 2. At the moment I am running it switched to low so it has 55k on it. So, I wonder, in my amateurish way whether the input signal needs to be attenuated a bit on tuner 1? At the moment the input is from either a PC sound card or a CD player.

I don't quite understand the microphone part of the tuner 1 input. I assume that the white lead that gets snipped is the dotted line between the switch contacts. If so the microphone signal would pass through R13R and C10R. That seems counter-intuitive as I thought a microphone signal was very weak. Because I can never resist an experiment I did try connecting a microphone to tuner 1 and got absolutely no sound with it at all.
Wage Slave is offline  
Old 25th Oct 2010, 10:08 am   #123
dave cox
Nonode
 
dave cox's Avatar
 
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,059
Default Re: Leak Delta 30 Amplifier - One Channel Down

I would think this is likely a symptom of C11 being a bit (electrically) leaky. Maybe C17 too, or even C12. The improvement over time / as it warms up is probably the cap re-polarising. Electrolytic caps with only a low voltage across them are prone to electrical leakage.

dc
dave cox is offline  
Old 25th Oct 2010, 10:36 am   #124
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

I changed C11 and C17 at Alistair's suggestion in the earlier repair. Of course that could mean a dry joint on my part. C12 sounds interesting. I have the parts so will try that when I get a bit of time. Thanks.
Wage Slave is offline  
Old 25th Oct 2010, 12:07 pm   #125
dave cox
Nonode
 
dave cox's Avatar
 
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,059
Default Re: Leak Delta 30 Amplifier - One Channel Down

OK, attach your meter across each cap and look for a slowly varying voltage corrisponding to the observed noise.

A 'freezer' spray might be useful in this situation to provoke the fault ...

Also, take a look around the switched (ac) feedback loop connected via C17. One thing to note is that oscillation / instability can exibit itself as noise.

dc
dave cox is offline  
Old 25th Oct 2010, 12:13 pm   #126
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

It seems that it is now appearing very reliably after it has been switched off for a while so that test should be pretty easy to do.

I know this sounds dim but how do I take a look at that feedback loop? Set the meter to volts AC and measure between earth and one end of C17 looking for instability in the reading?
Wage Slave is offline  
Old 25th Oct 2010, 1:09 pm   #127
Alistair D
Nonode
 
Alistair D's Avatar
 
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
Default Re: Leak Delta 30 Amplifier - One Channel Down

If the problem is cap related, swapping the preamp boards over should move the fault. Not wishing to cast aspersions on your work but is C11 reversed?

Al
__________________
I won't tell you how I discovered that.
Alistair D is offline  
Old 25th Oct 2010, 3:16 pm   #128
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

Quote:
Originally Posted by Alistair D View Post
If the problem is cap related, swapping the preamp boards over should move the fault. Not wishing to cast aspersions on your work but is C11 reversed?

Al
Yep. That is a good idea and it is of course possible I have the cap reversed.
Wage Slave is offline  
Old 30th Oct 2010, 6:31 am   #129
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

Well I swopped the boards over to see if the fault changed channels. It didn't. It just vanished. I suppose that must mean a poor connection where they plug in. Since they seem happier this way round I think I will just leave them like that and see how we go.
Wage Slave is offline  
Old 1st Nov 2010, 11:14 am   #130
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

Quote:
Originally Posted by dave cox View Post
I would think this is likely a symptom of C11 being a bit (electrically) leaky. Maybe C17 too, or even C12. The improvement over time / as it warms up is probably the cap re-polarising. Electrolytic caps with only a low voltage across them are prone to electrical leakage.

dc
Thanks for this Dave. I checked my installation of C11 and C17 and changed C12 on both boards. All seems fine now - time will tell.
Wage Slave is offline  
Old 7th Nov 2010, 5:12 am   #131
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

OK so I have changed all the electro caps on the pre-amp boards as I had bought them earlier. The distortion problem has gone as has some background hiss so it has done some good. I'm now thinking of changing the ones on the power amp boards as they are all the same type and vintage. I assume if I do this I should check/reset the bias. On the circuit diagram (above) it shows a point where it can be measured. The text underneath refers to shorting pins. I assume then that I take the shorting pin out, attach the meter across and then power up and adjust the current.

However, I cannot for the life of me find these pins. Does anyone know what they look like and where they are?

My other question is about one of the power capacitors. C6, 2,500uf 50V. It is huge and in an aluminium case with no plastic sleeve. Why is it so big? Is it a special type? I don't plan on changing it at the moment as there is no reason to think it is not doing its job but I am just curious. If it did need changing would a standard electro a tiny fraction of the size be fine?
Wage Slave is offline  
Old 7th Nov 2010, 12:35 pm   #132
'LIVEWIRE?'
Rest in Peace
 
'LIVEWIRE?''s Avatar
 
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
Default Re: Leak Delta 30 Amplifier - One Channel Down

C6 is just a standard can-type electrolytic. Replace with any suitable modern type-e.g
2200 or 3300uf 63v. These should be widely available from most of the usual suppliers.
They will be smaller in diameter than the original, so an additional screw hole will have to be drilled in the chassis, and a different mounting clip will be needed. Of course, if you are into capacitor stuffing(which I'm not!), and want to retain the original appearance, the old cap. could be cut open, contents removed, and a modern one fitted inside the can. There have been quite a few threads on this forum about how to do this.(sorry I don't have a link to any of them, but they should be findable via the Search facility at the top of the page)
'LIVEWIRE?' is offline  
Old 7th Nov 2010, 12:49 pm   #133
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

Thanks for that livewire. I was wondering about mounting. Modern caps are so much smaller! Modern 500ufs seem to about 13mm by 25mm. Even the smallest clip I can see on sale is too big by quite a way. What do people do? Wind some wire around the thing to pad it out?

I can't see me getting into cap stuffing with my current kit. I can see why people might do it with a piece of kit that is a bit special.
Wage Slave is offline  
Old 7th Nov 2010, 1:17 pm   #134
Alistair D
Nonode
 
Alistair D's Avatar
 
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
Default Re: Leak Delta 30 Amplifier - One Channel Down

Looking at the curcuit diagram doesnt show any pin numbers for the links. If they are there they will be close to the collector lead for T10 etc. The alternative way to do it is to disconnect the collector lead and insert your meter there(-ve probe to the lead, +ve to T10c).

C6 is the power supply smoothing cap. When this starts to fail the hum level will rise. I would only replace it if you suspect it may be faulty.
Re the size, try looking for a higher voltage version that will be in a larger case. Otherwise use something flexible to make a cuff. I dont think it will matter about an electrical connection between the cap and the mounting clip as I am sure it will have a insulated case.

Al
__________________
I won't tell you how I discovered that.
Alistair D is offline  
Old 7th Nov 2010, 1:36 pm   #135
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

Quote:
Originally Posted by Alistair D View Post
Looking at the curcuit diagram doesnt show any pin numbers for the links. If they are there they will be close to the collector lead for T10 etc. The alternative way to do it is to disconnect the collector lead and insert your meter there(-ve probe to the lead, +ve to T10c).
Yep. That sounds a pretty good way to do it - ta. I looked pretty well but will have another really close look at the board socket. I sort of suspect that it has been dropped from this version of the amp though.

Quote:
C6 is the power supply smoothing cap. When this starts to fail the hum level will rise. I would only replace it if you suspect it may be faulty.
Re the size, try looking for a higher voltage version that will be in a larger case. Otherwise use something flexible to make a cuff. I dont think it will matter about an electrical connection between the cap and the mounting clip as I am sure it will have a insulated case.
There isn't any noticeable hum so I will certainly just leave it for now. Just out of interest do the clips in general have a heat sink function or is it just a matter of achieving mechanical stability?

I know this is a really silly question but what does C34R, 1,000 uf 30V do? What would be the symptoms of it failing?
Wage Slave is offline  
Old 7th Nov 2010, 2:00 pm   #136
Alistair D
Nonode
 
Alistair D's Avatar
 
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
Default Re: Leak Delta 30 Amplifier - One Channel Down

The cap mounting clips are purely mechanical. Any kind of packing will do.

I am not surprised you are confused about C34R.

The panasonic amp you fixed had +ve and -ve supply rails with the common conncted to chassis(think of 2 batteries in series with the junction of the 2 batteries connected to chassis). The junction of the 2 output transistors is designed to be at the same voltage as the chassis so it is ok to connect the loudspeaker between this point and chassis.
Your Leak has only 1 supply rail so the common point of the outputs will be around 1/2 the supply voltage. C34 removes this voltage but still allows the sinal through.

C34 could fail S/C and put 24 volts across the speaker. Ouch. More commoly its capacitance will fall and take the volume with it. Bass frequencies will be affected first(capacitive reactance is higher at low frequencies).

Always fit a good quality part here.

Al
__________________
I won't tell you how I discovered that.
Alistair D is offline  
Old 7th Nov 2010, 2:15 pm   #137
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

Excellent answer. Got it! Many thanks.
Wage Slave is offline  
Old 10th Nov 2010, 12:51 pm   #138
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

How far can you increase the capacity of the speaker coupling capacitors without running into problems? I found some 6,800uf (original is 1,000uf) caps that are just about the right size to fit nicely. Size and lead diameter is important because there are hefty resistors hanging off them for the headphone socket. Modern 1,000ufs are less than half the size and have thin leads as they are designed to fitted to a PSB. So I am wondering .....

There are some more expensive specialist 1,000 uf audio caps the right size available from another supplier but I am trying to avoid two lots of delivery charges plus I am not sure that extra cost is justified. There are a lot of silly ripoffs around. What do people think?
Wage Slave is offline  
Old 11th Nov 2010, 12:36 am   #139
Alistair D
Nonode
 
Alistair D's Avatar
 
Join Date: Jan 2010
Location: Edinburgh, UK.
Posts: 2,008
Default Re: Leak Delta 30 Amplifier - One Channel Down

I would be concerned about the current level and the time the charging of 6800uF caps would take as this current passes through the speaker.

According to the front panel of my ESR meter, the ESR reduces as the rated voltage rises. I would consider looking for a higher voltage cap here that might be nearer the size you need but stick to the original value.

Personally I would not consider audio grade capacitors as I doubt that anyone could distinguish any sonic differences especially with modern electrolytic capacitors.

Knowing the work you have done up till now and what you are planning to do, I would consider looking for an ESR meter. I can talk you through all of the ins and out of using one if you need.

Al
__________________
I won't tell you how I discovered that.
Alistair D is offline  
Old 16th Nov 2010, 1:29 pm   #140
Wage Slave
Hexode
 
Wage Slave's Avatar
 
Join Date: Sep 2010
Location: Tsu, Japan.
Posts: 452
Default Re: Leak Delta 30 Amplifier - One Channel Down

This amp seems to be developing a new fault every couple of weeks. To be fair, I am running it a good 8 hours or more every day. Now I has a fairly loud crackling sound on one channel that lasts for about ten seconds on both power up and power down. It doesn't seem to be affected by the volume control or input switch.

Coupling capacitors? Bad connection between the amp boards and the sockets? I have cleaned them all but haven't tried tightening them up a bit yet and was suggested earlier.

Would it be better to hang off using it until the coupling caps have been changed which is scheduled in the next week anyway.
Wage Slave is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 9:20 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.