Lincoln L24 integrated tube amplifier

[ddrjboo]

I just purchased a Lincoln L24 integrated amplifier at an estate sale for $5. It appears to be in pretty good condition, but probably hasn't been operated in quite a while. It has nine tubes: (4) 6EU7s, (4) 6BQ5s, and (1) 6CA4. There are 2 canned multi-capacitors on the top side of the amp. One is a combo of 40 uF 400V, 30 uF 350V, 10 uF 300V, and 50 uF 25V. The second is a combo of (2) 10 uF 350V capacitors.

I am wondering how I should proceed with testing the amp out. I have a variac, but I read somewhere that the rectifier tube will not start passing voltage to the capacitors until it has reached some minimum voltage. Should I replace the multi-capacitors before supplying voltage to the amp? I think my options for replacing the multi-capacitors is to find a way to use individual caps instead, or "restuff" the cans myself, or send them off to be restuffed.

I would appreciate any advice on the best path to proceed, and also any information or experience that someone may have regarding this particular amplifier.

 

[maxhifi]

I just purchased a Lincoln L24 integrated amplifier at an estate sale for $5. It appears to be in pretty good condition, but probably hasn't been operated in quite a while. It has nine tubes: (4) 6EU7s, (4) 6BQ5s, and (1) 6CA4. There are 2 canned multi-capacitors on the top side of the amp. One is a combo of 40 uF 400V, 30 uF 350V, 10 uF 300V, and 50 uF 25V. The second is a combo of (2) 10 uF 350V capacitors.

I am wondering how I should proceed with testing the amp out. I have a variac, but I read somewhere that the rectifier tube will not start passing voltage to the capacitors until it has reached some minimum voltage. Should I replace the multi-capacitors before supplying voltage to the amp? I think my options for replacing the multi-capacitors is to find a way to use individual caps instead, or "restuff" the cans myself, or send them off to be restuffed.

I would appreciate any advice on the best path to proceed, and also any information or experience that someone may have regarding this particular amplifier.

First, have a look under the chassis, some coupling capacitors shouldn't be trusted, while others can be.

Have a look at my recent thread about re-forming capacitors, it's about a similar amp.

 

[ddrjboo]

Hi Max,
Thanks for your reply. I read your thread, and think I understand mostly what you did. I do think you did pretty much to your amp what I am trying to do with mine, and I hope I have the same success that you had.
Am I correct in that you used the variac to power up the amp with the tube rectifier in place? Or did you build a rectifier using the diode?
I added a picture of the amp from under the chassis, I am unsure how I can identify coupling capacitors. Can you provide me with where I should look to identify those? Also, is it you recommendation that I remove those and test them before applying power to the amplifier? I only have the capability now to measure the capacitance of them. I looked up a TO6, and it looks like a pretty useful thing to own to work on old electronics. I'm just not sure I want to spend the money for one at this time.
I am relatively new to this and am pretty much just a hobbyist with a lot to learn. Please forgive me if I ask too much or say something too naive.

 

[maxhifi]

Those four green guys under the chassis are most likely the coupling capacitors. I would change those first. To reform the capacitors, I used a 1N4007 in place of the rectifier, I described the procedure I used in detail, in the thread referred above.

Best regards

Max

 

[EastPoint]

Bring it up on a variac and it'll probably work fine. Don't change out those green caps. Those are really good caps and they will measure right on the money with no leakage.

 

[maxhifi]

They just looked like usual paper caps to me, if they're something else as Eastpoint says, you're in luck.

 

[EastPoint]

Those are Cornell Dubilier Greenies. They're special. They don't really drift or leak ever.

 

[primosounds]

There

Hi Max,
Thanks for your reply. I read your thread, and think I understand mostly what you did. I do think you did pretty much to your amp what I am trying to do with mine, and I hope I have the same success that you had.
Am I correct in that you used the variac to power up the amp with the tube rectifier in place? Or did you build a rectifier using the diode?
I added a picture of the amp from under the chassis, I am unsure how I can identify coupling capacitors. Can you provide me with where I should look to identify those? Also, is it you recommendation that I remove those and test them before applying power to the amplifier? I only have the capability now to measure the capacitance of them. I looked up a TO6, and it looks like a pretty useful thing to own to work on old electronics. I'm just not sure I want to spend the money for one at this time.
I am relatively new to this and am pretty much just a hobbyist with a lot to learn. Please forgive me if I ask too much or say something too naive.

There is an easy way to tell if the Greenie caps are leaking. Just measure the voltage on el84 grid that the cap is coupled to when you are using the variac. There should be no DCV there. If the meter reads a steady DC , then the cap is leaking. If one capis leaking you should change them all to keep the sound quality similar.

 

[ddrjboo]

I appreciate all of the feedback! I just discovered that the tube placed in the socket where the 6CA4 rectifier goes is actually a EZ80/6V4, which I read is a lower amperage tube. I also read that I can use (2) 1N4007 diodes to replace the rectifier by putting the anodes of one in pin 1, and the anode of the other in pin 7, and put the two cathodes from the diodes in pin 3. That sounds easy enough. I believe the difference will be higher voltage output than the tube would have provided, but I should be able to control that with the variac, and never actually proceed all the way to 120 volts AC.
If any of this seems wrong, please chime in. I will probably try this out tomorrow unless I hear a reason why I shouldn't. I will also test the capacitors as suggested by primosounds.

 

[primosounds]

I appreciate all of the feedback! I just discovered that the tube placed in the socket where the 6CA4 rectifier goes is actually a EZ80/6V4, which I read is a lower amperage tube. I also read that I can use (2) 1N4007 diodes to replace the rectifier by putting the anodes of one in pin 1, and the anode of the other in pin 7, and put the two cathodes from the diodes in pin 3. That sounds easy enough. I believe the difference will be higher voltage output than the tube would have provided, but I should be able to control that with the variac, and never actually proceed all the way to 120 volts AC.
If any of this seems wrong, please chime in. I will probably try this out tomorrow unless I hear a reason why I shouldn't. I will also test the capacitors as suggested by primosounds.

That is what you would do when using a variac with a tube rectified amp. There are also SS replacements for the 6ca4 which would be easier than installing the diodes. I am sure they are on epay as well other distributors.

 

[Dandy]

I wouldn't start by replacing the EZ80 with diodes though what you describe will work if you monitor the voltage.

Just get a 6CA4 or EZ81. It may work okay with the EZ80 for a while.

The filter caps in the cans will probably need replacement for regular use.

 

[Tom Bavis]

The EZ81 is barely adequate for a 6BQ5 amp, EZ80 is not. SS rectifier will increase voltage, of course, but that can be handled with a dropping resistor.

It's possible that the amp was made by a better-known company, and it's usually possible to find from the transformer numbers. Post them here.

 

[Erhard-Audio]

you should actually be able to get the amp working fairly well with about 70-80V on the variac, at least to see, and hear, and smell..... if there are any issues.
And yes, use specified tubes, or at least, close equivalents to them for the rectifier tube. Once you've established that the amp is more or less OK, I would then probably replace those power supply can caps as a matter of course and do a good visual check over, then bring the amp up to 110V full operation.
You can always go solid state rectifier at a later stage. But if you do, yes, raw B+ will be much higher and will need to be brought back down to spec B+. Before you even go there though, you will need to work out what the total B+ current draw is so that you can work out the correct resistance, and more important, the wattage of that drop down resistor. You do that with the amp in OEM configuration. It could very well be, that the drop down resistor will need to be quite a high wattage to handle total B+ current draw.

 

[Dandy]

The EZ81 is barely adequate for a 6BQ5 amp, EZ80 is not. SS rectifier will increase voltage, of course, but that can be handled with a dropping resistor.

Can you expand on why an EZ81 is barely adequate here? Should the OP save cash and go down the SS route right away?

 

[ddrjboo]

All the information and advice is great! Thanks.
So, to provide a temporary fix, I used the two 1N4007 diodes in the rectifier socket, and slowly ramped the ac power while monitoring the dc voltage in various spots. When I got up to 85 Volts ac, the dc from the diodes was about 250 Volts. No smoke or flames! Leakage voltage at the Cornell Dubilier caps was varying between about - 2 mV and +3 mV . I would appreciate opinions if that is good or means they should be replaced.
Then I turned off the varister and waited until today. Today I put in all the old tubes except the rectifier (still had the diodes in), and gradually turned up the ac. At 90 Volts ac, I was getting 250 Volts dc. Still no smoke! And the tubes were glowing.
I connected some speakers and an audio source to the tuner input. To my amazement, it's working!
I am going to clean all the pots, and look into replacing the canned capacitors, and order a rectifier tube. I may also want to switch to using 12ax7s with socket adapters.
There's no ground connection for turntables. Any suggestions?

 

[ddrjboo]

The EZ81 is barely adequate for a 6BQ5 amp, EZ80 is not. SS rectifier will increase voltage, of course, but that can be handled with a dropping resistor.

It's possible that the amp was made by a better-known company, and it's usually possible to find from the transformer numbers. Post them here.

The two smaller transformers are TO-110, and the larger transformer is TP-19L.

 

[ddrjboo]

you should actually be able to get the amp working fairly well with about 70-80V on the variac, at least to see, and hear, and smell..... if there are any issues.
And yes, use specified tubes, or at least, close equivalents to them for the rectifier tube. Once you've established that the amp is more or less OK, I would then probably replace those power supply can caps as a matter of course and do a good visual check over, then bring the amp up to 110V full operation.
You can always go solid state rectifier at a later stage. But if you do, yes, raw B+ will be much higher and will need to be brought back down to spec B+. Before you even go there though, you will need to work out what the total B+ current draw is so that you can work out the correct resistance, and more important, the wattage of that drop down resistor. You do that with the amp in OEM configuration. It could very well be, that the drop down resistor will need to be quite a high wattage to handle total B+ current draw.

I'm impressed by your custom amps!

 

[Erhard-Audio]

I'm impressed by your custom amps!

thank you, appreciate your positive comment!

 

[Erhard-Audio]

The EZ81 is barely adequate for a 6BQ5 amp, EZ80 is not. SS rectifier will increase voltage, of course, but that can be handled with a dropping resistor.

It's possible that the amp was made by a better-known company, and it's usually possible to find from the transformer numbers. Post them here.

the EZ81 is the same as the 6CA4. Looks like max current is about 150mA with a voltage drop of 20V. Filament 6.3V @ 1A. So if the 6CA4 is an OEM spec, then the EZ81 should be fine, as long as total B+ does not exceed 150mA or so.

 

[ddrjboo]

There

There is an easy way to tell if the Greenie caps are leaking. Just measure the voltage on el84 grid that the cap is coupled to when you are using the variac. There should be no DCV there. If the meter reads a steady DC , then the cap is leaking. If one capis leaking you should change them all to keep the sound quality similar.

Leakage voltage at the Cornell Dubilier caps was varying between about - 2 mV and +3 mV . I would appreciate opinions if that is good or means they should be replaced.