trio W-38 problems

[damianl]

Hi just wondering if anyone has information, circuit diagram, manual ANYTHING on a TRIO W-38 valve amplifier/reciever. Just aquired one for $20 ,lt works fine except one valve (a 6bm8) is overheating (the metal inside glows red hot) Im told this is due to voltage bias. I know what this means but not how to change this. Im told its a resistor at pin 6 of a 6bm8? Its in rather bad physical condition although i will be restoring this, is it a good idea to just go ahead and replace everything. Or not worth my time.

[anatech]

Hi damianl,
My money is on a leaky coupling capacitor. Capacitors are something you would normally replace on an older device like yours. The very small mica or ceramic capacitors don't need changing, just the filter caps and the coupling capacitors. They generally range between 0.001 uF to 0.22 uF in value. Try to replace them with the same value capacitor as they were.

It's probably worth repairing the unit.

-Chris

[damianl]

Thanks i will try that by the looks of the caps they are dead. Btw i ahve an old pioneer amp thats very similar (same valves) with the same problem BUT there is also hum through the speakers would this hum be the filter caps?

Btw anyone know what this trio amp would be worth fully restored? (although im not going to be selling it for many years)

Thanks

[damianl]

Hmm couldnt edit my first post but anything on the trio amplifiers models "w-20 to w-50" should be fine too if someone has anything. Not sure if those models exist but i do know there is a w-20, w-35 w-40 and they are very very similar inside so any models around that should work.

Thanks

[anatech]

Hi damianl,
Trio is bettre know by it's current name. Kenwood. So you have early Kenwood product.

there is also hum through the speakers would this hum be the filter caps?

This could be filter caps, or one output drawing too much current. You would find an oscilloscope very handy right about now.

-Chris

[tubelab.com]

When I worked as a repair tech in a stereo shop 1970 - 1972 many of these units carried both names, or the box said Kenwood, and the actual unit said Trio. I think that this was similar to the Akai - Roberts deal. One was "Fair traded" (price controlled) and one was not.

Either way schematics were impossible to get then if you were not an authorized dealer. A unit of that age probably needs all critical capacitors replaced, and all resistors at least ohmmeter checked. Same deal with the old Pioneer. If any tubes are glowing, the excessive current draw can cause the hum, by unbalancing the current through the output transformer.

[damianl]

Yeah this thing has markings from kenwood and trio too. although the kenwood version of this amplifier seems really rare.

Hmm I will go and replace every single capacitor in fact looking at it right now 2 of the coupling caps are blown (there reverse ended ones + top - bottom and they are starting to bulge).

Does anyone know where to get some "old?" elna caps 150wv 40uf and 0.05uf, 400wv. Would prefer origonals Otherswise what are some good quality replacements.

Since the caps have died i should be replacing every component after say the coupling caps eg if they are dead they could have blown resistors afterwards etc.

This red hot valve whats the heat do to its life? will it blow much much quicker? Because it had this thing running fine for an hour or so until i noticed it was too hot and it didnt seem to have any problems .. (you can quess what im thinking thats really dangerous and bad for the amp isnt it)

Thanks for your help guys

[SY]

If you're using the amp for music and not restoring for sale to a collector, don't bother with old Elna caps. A good quality modern polypropylene/foil will be far more reliable. I like the Wima FKP, but there are a lot of other good choices, too.

Don't try to salvage the abused tube- it's cheap, just toss it and put in a new one.

[damianl]

THats exactly what im doing gonna be using this amp. Although im restoring it to look brand new, not neccesarily the same colors and design. I will also be ripping the tuner from this as i wont be using it and replacing the front panel with one of my "Cahill audio" ones (the brand under whitch i sell amplifiers). Fun project!

Btw higher quality caps have a longer life correct?

Anyone know whereabouts in australia i could source these Wima FKP's or any other hign quality components.

Anyoone know much about these and if they are worth me buying:
http://cgi.ebay.com.au/VALVE-TUBE-AM...QQcmdZViewItem

Thanks

[damianl]