opinions wanted - Lafayette Stereo 224 Tube Amp

[loomis]

Hi. I also posted this over at audiokarma. I'm not sure why this is showing as my first post, I thought I had posted here a few times before.

I am a relative newbie to tubes. Recently I acquired a super-clean Layfayette Stereo 224 integrated tube amplifier. The build quality is very good. Tubes are 6gw8 's, 12ax7 's, and a 5ar4.

What can you guys tell me about it? Google was not my friend. Isaw a few things on this site, but not a whole lot. It's not the 224a or 224b, just the 224. Never seen one on ebay.

The bass, treble, and volume pots are all double pots (with a left and right knob on each one) which is quite annoying. Moreover, the volume pot is also the on/off switch. I'd like to bypass the tone controls and have one volume knob and a separate power switch. Thoughts?

Anyone have a schematic? What else would you guys recommend doing to get started?

Thanks. Picture links below.

http://home.neo.rr.com/bughead/lafayette2.jpg
http://home.neo.rr.com/bughead/lafayette3.jpg

[SY]

Wow, that IS super clean! Nice pick-up. I would be tempted to just replace e-lytics, tubes, and any selenium rectifiers in there and leave it stone stock.

[anatech]

Hi loomis,
I'm with SY one this. Nice unit. Just fix the problems and parts that we know will fail. Leave it stock otherwise. The tone controls will not hurt you.

It's rare to find a unit in such good shape.

-Chris

[kevinkr]

I have had several Lafayette and Realistic stereo amplifiers and tuners of this vintage, you will need to replace those nice looking coupling caps in fairly short order unless the thing has been stored in a very dry environment for a long time.. They are paper in a nice aluminum can and get leaky very quickly once pressed back into use. (Damaging output tubes.) I have never had to replace one of those electrolytics yet, although that is not a bad idea either.

Nice find.

Kevin

[loomis]

Ok sounds good. Thanks for the input. I will leave it stock except for the couplers and any others that are prone to failure. Thanks again.

I just wish I could find a schematic for it. That would help me a lot. Thanks

[grrr]

I have a 224B the front looks differend but the electronics is excacly the same. it is a nice amp. it is even somewhat famous by audiofiles in holland. A lot of them were sold here i suspect there was a article in a old audio magazine using the trannies for diy. I like to keep it as it is it is a bit of history.

[tubelab.com]

I can't quite make it out in your picture but it looks like this amp has two of the suspect caps connected from either side of the power line to chassis ground. The ones mounted right on the power transformer. This was fairly common in those days. If the amp has a two wire power cord (also common), the chassis (and the rest of your system) could become connected to the power line if one of these caps fails.

I recommend installing a three wire power cord that positively grounds the chassis. If originality is important, use an external ground wire. I would also remove these 2 caps, or replace them with high quality parts.

[loomis]

Tubelab:

By golly I think you are right! I'm gonna email you this post as well.

There are indeed 2 caps coming off the 0 and 115v at the power transformer, right after the on switch. They cross over the transformer and both go to the pin marked "E" on the other side of the transformer, which I believe is "earth" or ground correct?

What are those caps for? So it's safe to just take them out completely?

here's a pic: http://home.neo.rr.com/bughead/lafayette6.jpg

As far as wiring a 3 prong power cord, where does the ground go, to the E ground on the tranformer, or just to a bolt holding the power transformer down? And then the hot goes through the fuse and then to the 115v on the tranny, and the neutral goes through the on switch and then to the 0v on the tranny correct?

Unfortunately my outlets aren't properly grounded I don't think. I have a feeling the only 2 that are three-prong are grounded to neutral or to the box itself or whatever (apartment). Amp should still be given a 3 prong cord though anyhow, correct?


Thanks!!!

[tubelab.com]

The E terminal on the transformer should be connected to the chassis ground. I can't follow the black wire coming form the 0 terminal of the transformer but I suspect that it goes to chassis ground.

When adding a 3 wire cord I connect the 3rd (ground) wire (usually green with a yellow stripe) to chassis ground. The other two wires connect to the same points that the original power cord connects to. There is some difference of opinion as to what the proper connection of the other two leads are. My preference is to put the switch in the hot lead.

The caps were originally for power line noise filtering. Some people claim that they help when using a 3 wire grounded cord, and some claim that they cause a buzz or hum. It depends on your power line noise situation. If it is possible that your outlets are not properly grounded, I would not use them.

You can check for continuity ( ohmmeter) between the ground pin on an outlet and a metal water pipe (if you have metal plumbing) in the kitchen or bathroom. If there is a few ohms or less then the outlet is OK.

[kevinkr]

If you think that your outlets are not properly grounded I would not connect anything with a 3 wire cord to them!

When I had my house rewired (lots of knob and tube plus BX) the electrician and I discovered several outlets where someone had connected the wiring neutral to both neutral and ground on the outlet . At best the IR drop across neutral would raise the chassis several or more volts above ground, at worst should a connection fail in the neutral wire anywhere on that circuit you could end up with the full line voltage on the chassis through the shared neutral/gnd connection on the outlet. This happens because most devices connected across the line are not going to have very high internal impedances. (Light bulbs, transformers, etc.)

IMHO You would be better off in this case just removing the capacitors from chassis ground to the ac power line.

You can check for leakage to chassis with a 100K resistor and a dvm. Connect meter in parallel with resistor, connect one end to chassis and other to KNOWN good ground. (Water pipe or whatever.) 100uA leakage current will result in 10Vrms across the meter. Find the ac plug position that gives the lowest reading. If you measure leakage much higher than this you should ground the chassis for safety. (Or you can use an isolation transformer to power the amp.)

Using an ohm meter and measuring from a known ground to the ground on an outlet is not the whole story (it did not detect the subterfuge on my outlets) - you may have continuity, but you need to make sure that there is no voltage difference to be sure that you actually have a viable ground, and finally if you are comfortable doing so take a look at the outlet itself or hire an electrician to check it out for you..

As a final note I am not an electrician or inspector, and nothing I or anyone else say on this forum should be taken as gospel, consult a professional if in doubt.

Kevin

edit: fix typos add additional caution