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PostPosted: Tue Sep 12, 2017 3:52 pm 

Joined: Sun Jan 16, 2005 7:39 pm
Posts: 180
Location: Kitchener, ON, CA
I am in Kitchener and could test the tubes for you.

flo777 wrote:
I assume that the old Electrohome amp and preamps from consoles are fixed bias.
So if all that takes to restore an old tube amp is replace the caps and tubes that need replacing, besides cleaning the pots, then I can attempt that. Is there something important that I am missing?
I would just need to buy a tube tester

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PostPosted: Tue Sep 12, 2017 9:09 pm 
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Joined: Sat Sep 10, 2005 11:49 am
Posts: 2999
Location: A-Tube-O-Coke, ON, CA
sasquatch wrote:
Yes fixed bias with a DC hum balance pot.
If you're comfortable go for it.Make it a thread.
Could get by without a tube tester.

My preliminary rule of thumb:
How old is it, and when was the last time it was known to work?
I wouldn't worry too much about the tubes for now.

You'll need a DMM. Not necessarily an expensive one, all you're going to use it for is continuity and rudimentary resistance and potential voltage checks. (Pun intended) :D
Oh, a soldering iron and some Rosen core solder. Hobbyist stuff, you can upgrade later if you find that your having fun
Get the schematic. It will be your best friend, and make notes of any changes you may make that vary from the schematic. If you end up taking it to a tech he'll appreciate it.

Use the schematic to start identifying all the parts in the chassis, and start making continuity tests starting at the power transformer secondaries. (Seeing that some tubes are lit, we know that the primary and fuse are good for now.)
Concentrate first on the tube heater circuits. They're heated by AC, but both legs of the heater transformer are marked "X" on the schematic, so you sort of have to figure out which tube socket pins are for the heaters. There should be continuity between either leg of the hum balance pot to either of those heater pins at all tube sockets. The heater circuits are well marked on the schematic. (I highly recommend printing out the schematic. Apparently, Staples will print out a poster sized PDF for a few bucks. Great for making notes on.)

Which tubes are lit, and which tubeside are dark? Maybe that info can make this part of it easy.
An interesting thing: I see a pilot light, but I don't see a power switch. Something I'm not seeing here? The fuse says "some models only". Has this thing got a power umbilical to another device and I'm looking at the wrong schematic? Been known to happen :lol:

I agree, start a thread. This could be fun and educational.

Of course if you're in a hurry there's no shame in letting a pro look at it instead.

Hunt down a variac. It's an essential tool for restoring old equipment. Nothing fancy. When you go to power up, you can do it gradually and shut it down if any smoke tries to escape.

"There are some people who, if they don't already know, you can't tell 'em."
Lawrence Peter Berra (1925-2015)

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PostPosted: Tue Sep 12, 2017 9:16 pm 
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Joined: Sat Feb 23, 2013 10:41 am
Posts: 8393
Location: Burlington, ON, CA
I bought a new variac at Sayal a couple years back, my recollection it was a hundred and a half.
For caps and stuff a good tech like Dan is very reasonable. Most techs won't take trades out of the gate because they probably get stuck with a lot of stuff guys couldn't pay for.
If you can't afford it, sell it as is, or park it in your basement. And maybe ask yourself is it worth it?

"In theory, everybody tells me I'm not under investigation!"

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