Lincoln L24 integrated tube amplifier

[Leben]

I’m enjoying following this thread. I picked up a Lincoln L24 a while back and have been trying to find any info on it that I could. It looks like this integrated was badged under several names such as Knight 735 and Grommes (20-lj?). Mine has an Allied Radio Corp sticker on the back. There seem to be some slight variations between models but they look to be pretty much the same.

I tested mine with a variac and ordered some new parts to install, including custom can caps from Hayseed Hamfest. You will likely get yours completed before I start on mine. Yours looks really clean and seems to be in great shape. Best of luck with your project!

 

[Leben]

An odd thing about mine is that the on/off switch is part of the treble control. I’ve never seen anything quite like it.

 

[ddrjboo]

An odd thing about mine is that the on/off switch is part of the treble control. I’ve never seen anything quite like it.

Yes, that is quite unique!

 

[ddrjboo]

I’m enjoying following this thread. I picked up a Lincoln L24 a while back and have been trying to find any info on it that I could. It looks like this integrated was badged under several names such as Knight 735 and Grommes (20-lj?). Mine has an Allied Radio Corp sticker on the back. There seem to be some slight variations between models but they look to be pretty much the same.

I tested mine with a variac and ordered some new parts to install, including custom can caps from Hayseed Hamfest. You will likely get yours completed before I start on mine. Yours looks really clean and seems to be in great shape. Best of luck with your project!

I've been looking at Hayseed Hamfest, too! What was the answer to the question on the custom quote form:
Polarity - Is the can common-negative or common-positive????
Do you already have a quote from them? If so, how much?

 

[crispycircuit]

I'd clip out the diodes and install the tube rectifier. Run it on the bench for a few hours checking the transformers & can caps for heat. If it all seems OK, then don't mess with it. It looks like a very nice amp....

 

[Leben]

I've been looking at Hayseed Hamfest, too! What was the answer to the question on the custom quote form:
Polarity - Is the can common-negative or common-positive????
Do you already have a quote from them? If so, how much?

I’ll try to find the receipt in the morning and let you know. Both cans were custom made so there was a little wait. Customer service was excellent and it is evident that they care about the product and customer. I like supporting specialty businesses like them so that they continue to be around. No affiliation, just a satisfied customer.

 

[primosounds]

Those readings, varying between + and - voltages are actually the music signal thru the cap. That indicates that the cap is behaving normally. That being said, i just replaced the signal caps on a Scott 222c which are well regarded "Ceracaps" which were testing good like yours. I replaced them because i felt the sound quality was a little soft or diffuse. I put in some Sprague "orange drops" which did make the sound a little more focused and float in front of the speakers. In other words the soundstage improved.

 

[maxhifi]

Yes, that is quite unique!

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.

They are not leaky, they are good.

 

[Leben]

I've been looking at Hayseed Hamfest, too! What was the answer to the question on the custom quote form:
Polarity - Is the can common-negative or common-positive????
Do you already have a quote from them? If so, how much?

Pm sent with Hayseed info.

 

[ddrjboo]

I'd clip out the diodes and install the tube rectifier. Run it on the bench for a few hours checking the transformers & can caps for heat. If it all seems OK, then don't mess with it. It looks like a very nice amp....

The amp seems to run fine with the EZ80/6V4 rectifier, and it glows very nicely! In your opinion, what problems, if any, could using the lower amperage rating tube cause (shorter tube life, fire, explosion, the end of the world as we know it???)? There is no heat coming from the canned caps.

 

[Erhard-Audio]

The amp seems to run fine with the EZ80/6V4 rectifier, and it glows very nicely! In your opinion, what problems, if any, could using the lower amperage rating tube cause (shorter tube life, fire, explosion, the end of the world as we know it???)? There is no heat coming from the canned caps.

well the EZ80 is rated at 90mA as compared to 150mA for the EZ81, quite a difference. What needs to be established is what the total B+ current draw of this amp is, then it can be correctly determined if the EZ80 is OK or not.

 

[ddrjboo]

well the EZ80 is rated at 90mA as compared to 150mA for the EZ81, quite a difference. What needs to be established is what the total B+ current draw of this amp is, then it can be correctly determined if the EZ80 is OK or not.

So it's easier for me to just to get the OEM rated tube. I am just trying to learn here. Is it possible the amp is drawing more than 90 mA from the rectifier, causing it to work harder than it is designed to, or something else? Also, if I wanted to measure the B+ current draw, would I need to put the ammeter in series with the positive lead coming from the rectifier tube, and have the amp playing at a reasonably high volume? Thanks for sharing your expertise with a novice.

 

[Tom Bavis]

Very likely that the amp needs more than 90 mA from the rectifier. EZ80 won't last long.

The Grommes 20LJ used the power transformer TP19, and output transformers TO-10. Sounds pretty close! Power transformer is rated 100 mA, according to Sams, which would be a measured current. I'd say the transformer is good for 150 mA, based on winding resistance.

Email for a scan of the 20LJ - tbavis(at)rochester(dot)rr(dot)com

 

[Erhard-Audio]

So it's easier for me to just to get the OEM rated tube. I am just trying to learn here. Is it possible the amp is drawing more than 90 mA from the rectifier, causing it to work harder than it is designed to, or something else? Also, if I wanted to measure the B+ current draw, would I need to put the ammeter in series with the positive lead coming from the rectifier tube, and have the amp playing at a reasonably high volume? Thanks for sharing your expertise with a novice.

I would have to agree that the amp probably draws more than 90mA. The best way to measure current, in this case, is to get a 10 OHM 1W resistor, one end goes to the tube rectifier output and the other end to the B+ input, where the output of the tube rectifier normally gets connected to, with other words, in series with the incoming B+. Set your meter to say 10VDC and measure the voltage ACROSS the 10 OHM resistor and post the result here. This is, in my opinion, a better way than to put the meter, set to AMP's, in series with the rectifier B+ output.
So, say you read 1.2V on the meter, using OHM's law, I=V/R, current = voltage divided by resistance, in this case. I = 1.2/10 = 120mA/0.12A
Wait at least 1 to 2 minutes before you measure across the 10 OHM resistor to allow B+ to come up to operating voltage.

 

[gadget73]

Typical 6bq5 conditions at 250v want 138 ma for 2 channels at idle and 180 ma at full scream. At 300v its 160 ma at idle and 228 at full output. Thats plate + screen current. There is also the driver circuits to account for, I'd guess another 10ma for that.

So basically thats why a 6CA4 isn't quite adequate for a stereo 6bq5 amp, and why a 6V4 is grossly inadequate.

of course it could be biased cooler to make up for a weak power supply, but expect less power and worse distortion performance because of it.

 

[mhardy6647]

Yes, that is quite unique!

Several EICO integrated amplifiers did that as well. The HF-12 is one example that pops into mind.

(borrowed photo)

This titular Lincoln is not an EICO, though.

Lincoln was a low-end brand name sold by Allied. Most of the Lincoln branded stuff, I think, was Asian (Japanese). Not sure about the titular amplifier, though. The morphology doesn't scream Japanese to me (although it does sort of subtly whisper it).

 

[crispycircuit]

I can't see you running this amp at full volume, nor was it made for that. If the amp lasted this long, I doubt there is any problems with the design. If the cap cans don't get hot, they should be OK. Power transformer will get hot, it's normal. When your smell something cooking, then look for trouble. It's a nice amp enjoy it......

 

[ddrjboo]

I would have to agree that the amp probably draws more than 90mA. The best way to measure current, in this case, is to get a 10 OHM 1W resistor, one end goes to the tube rectifier output and the other end to the B+ input, where the output of the tube rectifier normally gets connected to, with other words, in series with the incoming B+. Set your meter to say 10VDC and measure the voltage ACROSS the 10 OHM resistor and post the result here. This is, in my opinion, a better way than to put the meter, set to AMP's, in series with the rectifier B+ output.
So, say you read 1.2V on the meter, using OHM's law, I=V/R, current = voltage divided by resistance, in this case. I = 1.2/10 = 120mA/0.12A
Wait at least 1 to 2 minutes before you measure across the 10 OHM resistor to allow B+ to come up to operating voltage.

I had a 10 ohm, 2.5 watt resistor that measured 10.6 ohms with my meter. I set up the resistor as you specified. The voltage across the resistor was 0.93 V. I get I = 0.93 V / 10.6 ohms = 0.087 amps. So does that mean the rectifier is only capable of .087 amps, or is that all the amp is "asking for"? Please pardon my lack of proper terminology! Would the .15 amp rectifier provide a better sound? Again, I am replacing the rectifier anyway, just hoping to learn here.

 

[ddrjboo]

Typical 6bq5 conditions at 250v want 138 ma for 2 channels at idle and 180 ma at full scream. At 300v its 160 ma at idle and 228 at full output. Thats plate + screen current. There is also the driver circuits to account for, I'd guess another 10ma for that.

So basically thats why a 6CA4 isn't quite adequate for a stereo 6bq5 amp, and why a 6V4 is grossly inadequate.

of course it could be biased cooler to make up for a weak power supply, but expect less power and worse distortion performance because of it.

I love the knowledge available here, and the willingness to share it!

 

[Erhard-Audio]

I had a 10 ohm, 2.5 watt resistor that measured 10.6 ohms with my meter. I set up the resistor as you specified. The voltage across the resistor was 0.93 V. I get I = 0.93 V / 10.6 ohms = 0.087 amps. So does that mean the rectifier is only capable of .087 amps, or is that all the amp is "asking for"? Please pardon my lack of proper terminology! Would the .15 amp rectifier provide a better sound? Again, I am replacing the rectifier anyway, just hoping to learn here.

So that's 87mA, much lower than I expected.......this is what the amp is drawing on B+ at idle. Also, that is the current at idle. Once you 'crank it up' (as much as this amp could be cranked up ), that could go up by a couple of more mA. I assume all tubes were plugged in. So, in theory, the EZ80 could be used, but since it would be operated right at its max rating, not a good idea, so the EZ81 will be more than enough to handle this and will just sit there happily rectifying!