• Check out the Annual AK Secret Santa exchange Program, signup before November 23rd in the AK Charities & Christmas forum!

Lafayette Stereo 250A

Mike Stehr

Mike Stehr

Poverty Audio
This was a unit that was stashed in the back room for some time, and figured it was time to give it some attention. It's a little rough, with the usual chassis liver spots.

All the power supply caps were worn out, except for the negative bias supply decoupling cap can.
A dual section 60/60uF cap can was replaced with a NOS Sprague 50/60/60uF.

Out of spec resistors were replaced, and most all the decoupling caps, except a couple low value ceramics.
Pots were cleaned, most all the solder joints were touched up with some wire rearrangement, and ground points checked over.
Since the replacement snap-in caps from Mouser are much smaller, I had to get creative with perf-board and a little two part epoxy.

Of course like all the other Lafayette 250As, the unit only had around three knobs left. So I had to get creative again.
The 250A is ready to be powered up and checked over. But, the 6CW5/EL86 tubes that came with the integrated amplifier tested really low on a emission tester. And one is losing it's gettering, with little specs of white oxide floating about...it tested the lowest with regard to emission.

Fortunately, I have two Hammond labeled Sylvania 7199s that test good, and somewhat matched.
(how they test in circuit is different matter, however)

I do not have any spare 6CW5/EL86, so I ordered some. So the 250A is stashed for another week...
Er, the shot with the wiring...I wasn't quite finished yet...

Mike

DSCN2991.JPG DSCN3014.JPG DSCN3019.JPG
 
Register to hide this ad
Looking good, Mike. Nice roomy layout in this one--good to have some room to work. How hard was it to find the 6CW5/EL86 tubes? I though I recalled that they're getting scarce.
 
Cosmetically, yours is not so bad. the plating on the metal is not very durable or thick and corrodes easily. The face plate is decent too. This looks like it was made in Japan.
 
primosounds said:
This looks like it was made in Japan.
Click to expand...

I kinda doubt the Lafayette 250A were of Japanese manufacturing. I think the one I have is a kit, because there is some light pencil scrawling around underneath the chassis indicating #'s from the schematic. The capacitors, resistors, and pots used in the amp are all American brands...even the iron looks American made.

For reference here's the underside of Lafayette Model LA-55. A mono integrated EL84 PP amplifier which is definitely Japanese made. (wish I had another one of those OPTs)
DSCN3020.JPG
 
yeah it does look fairly US-made. Kind of interesting how the country of origin leaves a cosmetic "fingerprint" on the design of equipment. German and other Euro gear has a distinct but different look about it as well.
 
Ah ok. I thought by the design of the output transformer covers that it was made in Japan. That construction of the covers for the OPT reminded me of Japanese type. But, all the better, USA components are better in quality overall, and i am not demeaning the quality of Japanese vintage tube audio, which has steadily increased in collectibility and value over some of the other brands of its era.
 
My father had one of these amps. (I thought he assembled it himself.) As a kid, I remember being impressed with how it sounded. It has been sitting in storage since the 1990's.

I would be interested in your impressions once you get it finished.

I am wondering if it is worth paying someone to do an overhaul. (Probably too far from my skill set to rebuild.)

Here is a link to a magazine with a report on this amp:


http://vintagevacuumaudio.com/vintage-magazines/hifi/1961-7-hifi-stereo-review.pdf
 
Last edited:
Is there a link of a schematic of the Lafayette 250A that has voltage numbers listed? Like B+ voltage, plate voltages, etc...

The schematic I used has no reference voltages listed.

I am somewhat aware of how to adjust the balance/bias, with 48ma for each EL86. (0.48 volts)
And I'm guessing EL86 plate voltage of around 250-255 volts, with the screens around 200 volts...

It would nice to have some reference voltages to go by.
Thanks,
Mike
 
Mike Stehr said:
Is there a link of a schematic of the Lafayette 250A that has voltage numbers listed? Like B+ voltage, plate voltages, etc...

The schematic I used has no reference voltages listed.

I am somewhat aware of how to adjust the balance/bias, with 48ma for each EL86. (0.48 volts)
And I'm guessing EL86 plate voltage of around 250-255 volts, with the screens around 200 volts...

It would nice to have some reference voltages to go by.
Thanks,
Mike
Click to expand...
Mullard tube data recommends for 250 Av, 200 G2v, about 50ma Anode current.
 
Mike Stehr said:
Is there a link of a schematic of the Lafayette 250A that has voltage numbers listed? Like B+ voltage, plate voltages, etc...

The schematic I used has no reference voltages listed.

I am somewhat aware of how to adjust the balance/bias, with 48ma for each EL86. (0.48 volts)
And I'm guessing EL86 plate voltage of around 250-255 volts, with the screens around 200 volts...

It would nice to have some reference voltages to go by.
Thanks,
Mike
Click to expand...
Hey Mike, I just found this post, nice job on the KT-250A. I'm thinking seriously about finally rebuilding mine, I have a scan of the original KT-250A build booklet, but I assume this is what you have, and there are no listed voltages on the schematic. How do you like yours? It's a little strange, isn't it? I grew up with mine, my dad built it when I was pretty young, maybe 5 or 6 years old. It's followed me around since I left on my own in 1976!

At any rate, I'm sending you a PM...

Best,
Fran
 
In many of Lafayette's early Hi-FI equipment , the tube pin voltages, and sometimes even resistance measurements, were shown in separate charts in the manual along with information concerning hum, balance, and other initial setup adjustments. Check the manual not the schematic. Also, back in these "good old days" people servicing this equipment generally were fairly knowledgeable in what the typical voltages might be at a particular tube pin based on its usage in the circuit so schematic labeling of voltages at particular points wasn't always necessary.
I can't remember if the wired and tested versions were assembled in Jamaica, NY or NYC or both.
 
peteCWA said:
In many of Lafayette's early Hi-FI equipment , the tube pin voltages, and sometimes even resistance measurements, were shown in separate charts in the manual along with information concerning hum, balance, and other initial setup adjustments. Check the manual not the schematic. Also, back in these "good old days" people servicing this equipment generally were fairly knowledgeable in what the typical voltages might be at a particular tube pin based on its usage in the circuit so schematic labeling of voltages at particular points wasn't always necessary.
I can't remember if the wired and tested versions were assembled in Jamaica, NY or NYC or both.
Click to expand...
You're right, thanks. I forgot that's where the voltages can be found.They're listed on pg. 53 of the assembly booklet I have.

IMG_20160523_0053 (Large).jpg
 
Back to this project...Thanks again to Fran604g for the assembly/instruction manual. That helped a bunch.

I had a problem with voltage to a couple 12AX7s, (V1/V6 I think) as in no voltage. And the indicator light didn't work.
The can capacitor I used had a bad/leaky 60uF 300volt section, along with a open wire-wound 8.2K 1 watt resistor.
So I jeeped in a 68uF 400volt radial, and a 8.2K (8K measured) 1 watt carbon composition because it's what I had.

Everything seems to measure up close-enough for the plus or minus 15%.

I'm using 12AX7 that were just tossed in, and need to use some more matched/stronger 12AX7.

The bias was dialed-in according to the manual procedure. One pair had a bias voltage right at .45 millivolts and input grid voltage of -19 to -20.
The other pair would bias at .45 millivolts, but the input grid voltage was -23 to -24 volts. I really need to determine bias current instead of voltage and total dissipation.
One tube seems to have a hot spot on the plate, but I did buy used EL86 on the cheap.(Amperex) I might switch pairs from each side, and see if the one EL86 still has a red spot.
If so, I'll have to order some more used cheap Amperex EL86.

Still noodling...

DSCN3561.JPG
 

Attachments

  • DSCN3546.JPG
    DSCN3546.JPG
    157.6 KB · Views: 46
Last edited:
Mike Stehr said:
The bias was dialed-in according to the manual procedure. One pair had a bias voltage right at .45 millivolts and input grid voltage of -19 to -20.
The other pair would bias at .45 millivolts, but the input grid voltage was -23 to -24 volts. I really need to determine bias current instead of voltage and total dissipation.
One tube seems to have a hot spot on the plate, but I did buy used EL86 on the cheap.(Amperex) I might switch pairs from each side, and see if the one EL86 still has a red spot.
If so, I'll have to order some more used cheap Amperex EL86.
Click to expand...
All voltages read, and in the voltage chart, should be in volts. If you're reading .45 millivolts, that's not good. .45 millivolts is 0.00045 volts.
 
peteCWA said:
All voltages read, and in the voltage chart, should be in volts. If you're reading .45 millivolts, that's not good. .45 millivolts is 0.00045 volts.
Click to expand...

Error on my part, indicating millivolts. I had the meter set for the 2 volt scale. So it would be .45 volts.
 
Mike Stehr said:
The bias was dialed-in according to the manual procedure. One pair had a bias voltage right at .45 millivolts and input grid voltage of -19 to -20.
The other pair would bias at .45 millivolts, but the input grid voltage was -23 to -24 volts. I really need to determine bias current instead of voltage and total dissipation.
One tube seems to have a hot spot on the plate, but I did buy used EL86 on the cheap.(Amperex) I might switch pairs from each side, and see if the one EL86 still has a red spot.
If so, I'll have to order some more used cheap Amperex EL86.
Click to expand...
-19 to -20 volts on the grids of the output tubes is good. Note that the cathode resistors are 10 ohms at +/-1%. After aging for 50 years and passing current, it's possible the resistance has drifted out of tolerance which would screw up the .45 volt reading.
If a tube is drawing too much current, a red plate glow or "red spot" on the plate can indicate a tube of poor quality and sometimes can also indicate that the coupling capacitors from the previous stage (in this case the 0.1 mfd's) to the grids of each output tube are leaking passing a positive voltage to the grids, further screwing up both the grid and cathode voltages.
 
You must log in or register to reply here.
Back
Top Bottom