Lafayette Stereo 236A Re-Cap questions

[Zephedone]

I'm in need of a little advice on recapping this little amp . I fired it up and used it for a few hours and it sounds great . Did a little clean up of the pots and switches so no "crackle" or other weird noises . It seems to be working fine (although the power tranny seemed to get hot) but I want to do a cap job as it is overdue I'm sure . I think the power supply uses a voltage doubling circuit and maybe that has something to do with the hot power tranny . I found a little info on a similar model that also seemed to run hot possibly due to the doubling circuit . Anyway the replacement of the caps needs to be done and I was wondering if there is a way to do the doubling circuit without purchasing those highly expensive can capacitor types .

[pops]

If you can find room you can substitute individual caps for the caps in the cans, but you will need to be very creative to get them all in and you will need to disconnect the cans and find anchor places for all the caps. If it was only one can i would use individuals, but sometimes there is only one cap in a can or three and you can get a can with four and use the extra cap. You can be creative and use both to make it work out the best way or just get new cans.

[gui_tarzan]

I did this with a Pioneer recently. A couple of the cans were still available, I think one had an extra cap in it which just sits unused. Two of them were not available in the right configuration so I hollowed out the original cans and put them inside with some black permatex to hold them in. The owner liked that idea because it kept it looking original but was still updated.

[xtian]

Radial caps are easy to cram into small spaces. Here is a cap job I did on a 60s Sano. I left the cans in place, but snipped out the old solder tabs to make room for the radials.

[Stevem]

If that amps output tubes are cathode biased then be sure to check those two cathode resistors as if they have drifted down in value the tubes will be pulling more current and in turn make the PT run hotter than it should!
It's also not a bad idea to change them just for the fact of upping there wattage by one or two watts to end up with a more stable output stage.

A nice sonic up grade for guitar no less hi fi use is to change out all the Ciramic caps in the audio path for non-Ciramic types!

[Phil_S]

Ordinarily, I'd say go with single radial caps as the least cost solution and if you have space under the hood, why not? But this is such a nice piece, I think I'd be inclined to spend for the can caps.

What values are those? You should be able to find reasonable substitutes.

[Zephedone]

On top of the chassis are three cans . The one wrapped in cardboard is 200mfd@25vdc . The one in the middle is also 200mfd@250vdc . This is the voltage doubler circuit I believe . The last can is 20mfd@350vdc and 150mfd@300vdc . The can near the preamp tubes reads 60/60mfd@250vdc . I need to locate a schematic for this as well . There are also three caps under the chassis but they are axial type and should be easy to replace . Also what is a good source for these parts .

[Phil_S]

Exact match isn't important. Voltage must be at or above what you have to be safe.

If you can deal with the on-line catalog at Mouser, that is where you are likely to find the most choices at much lower prices.

Looking at tubesandmore.com and tubedepot.com, 2 retail operations, you won't find those exact values. What I see are 50+50mf which should be fine for the 60+60mf can. I see 220@385V which should be good for the two 200mf and for the 150mf. The 20mf single should be easy but you may need to buy a 2 section cap. If you can get 10+10, you can wire in parallel, using a balancing resistor.

Remember the age of that amp. Back then cap tolerance would have been at least +/-20% and possibly +50%/-20%. That is the reason why I say exact match isn't important. You might want to write in Sharpie on the chassis the original values for the next guy.

[Zephedone]

Thanks Phil . I don't think there will be a next guy . Just the thought of going on the mouser site is giving me an anxiety attack . I will probably use one of your other suggestions . I went through the amp with a multimeter and the resisters all seemed to be pretty close but that was a while back . I'll get back into it this weekend and double check the cathode resisters as was suggested . I'll take some pics when I get to it . Maybe it will help someone else . Any Idea where I can get a schematic for this ? This thing sounded really good while I was testing it out . I have something else I need to re cap as well and I want to use this little Lafayette while I recap the amps in an old console that I have . I am enclosing a picture of the old console .

[Zephedone]

I went ahead and opened it up . A quick test with the multimeter and the cathode resisters test 135 and 149 ohms . The resister on the left is the one that drifted up . They are both marked 135R . So I need to replace at least one but will replace both when I replace those 100mfd @ 25 vdc bypass caps . It's a nice layout . Neat and tidy . I'm guessing this was a kit because most components are held on with nuts and bolts rather than rivets .

[Phil_S]

Tidy, indeed. That white 30mf cap bothers me. It doesn't seem to fit in. You really should replace that and all the other e-caps, too. They are all too old to be relied on.

I'm going to change my tune about the caps. I believe you have enough real estate in the neighborhood of the can caps to install a couple of long terminal strips. Make a plate to cover the holes where the cans are now. See if you can buy some modern axial caps and hang them on the terminal strips. If the useable distance is too narrow, then use those stubby looking radial caps. You'll need about 6-7" of space there and I think you have it. I don't think you have the width for axial caps. If the height is adequate, you might think about building a cap board with those stubby radials. Work the sub for the white 30mf onto the cap board.

You've got enough caps to buy that it is worth the headache on Mouser. Examples, not so hard to find:
http://www.mouser.com/ProductDetail/Nic ... o3Tw%3d%3d
http://www.mouser.com/Passive-Component ... x9Z1z0yp7w
http://www.mouser.com/ds/2/293/e-vy-11346.pdf

[Zephedone]

I think that's a good idea using terminal strips . How about the Pyramid signal caps ? Is there a way to test them for leakage ? If they are good is an upgrade really going to make that much of a difference in the sound ? Someone mentioned replacing the little disc caps as well . What is the advantage to their replacement ?

[Zephedone]

I found a schematic on someone's flickr account . I was also able to place an order for all but one of the filter and bypass caps . I am still looking for the 150@300 capacitor . I was able to keep the values real close to originals . I need to find a few terminal strips now . I measured the resisters and compared them to the schematic . I was wondering if someone would have a look at the differences and let me know if they are too far out of spec . I have a 500 ohm 3 watt resister that measures 579 ohms , a 6.8k 3 watt resister that measures 6680 ohms , a 6.8k 1/2 watt at 7580 , a 10k 1/2 watt at 10590 ohms and a 270k 1/2 watt at 289 k . The 270k 1/2 watt comes from the second to last node of the filter supply and is attached to the pilot lamp .

[Structo]

Man, that is a great piece of old gear.

There used to be a shop in my town that sold Lafayette gear and other types of audio gear.

Look how nice the lead dress is in the chassis.

It would be a joy to work on something like that.

[Phil_S]

I think that's a good idea using terminal strips . How about the Pyramid signal caps ? Is there a way to test them for leakage ? If they are good is an upgrade really going to make that much of a difference in the sound ? Someone mentioned replacing the little disc caps as well . What is the advantage to their replacement ?

An upgrade might not be that. I'd get it running right before even considering anything else. Search the forum for a discussion of how to test for leaky caps. It's been covered.
For Google, this is the search: leaky caps site:ampgarage.com
Some people are frustrated by what's lacking in the site's search feature.