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VARIAC: Procedure??? 2 old 30 wpc tube amps, unused for 4 years

Two Fisher 80Z, made 1958, overhauled 6 years ago, not used for 4 years

https://www.hifiengine.com/manual_library/fisher/80-az.shtml

Borrowed my friend’s VARIAC.

How many volts ___ to start?

Progress in ___ Steps?

How much time _____ each step?
.................................................

I found this, but always seek and welcome advice here

https://www.circuitspecialists.com/blog/using-a-variac-to-power-up-an-old-radio-or-amplifier/

says sniff/look for smoke while:

slowly dial up to 50V; 30 mins (pre-heat tubes; reforms electrolytic capacitors)

slowly                75V; 30 mins (power transformer/windings/drives out moisture)

slowly .............. 90V; 30 mins (if hum replace electrolytic capacitors) (old capacitors: replace em anyway).

slowly up to 110/120V
....................................................................


I’m gonna drop my Cayin off to have it’s internal bias adjusted by Steve at VAS

so, a chance to use these beauties (beautiful sound, actually hard lookers) with my McIntosh mx110z for the 1st time.

They will be driving the Electro-Voice speakers they were paired with in the 1958 Fisher President II I inherited. Always gives me good memories of my Uncle Johnny.

He had a fabulous apartment in NYC with one of a matching pair of Steinway Concert Grand Piano’s from the 1934 Chicago Worlds Fair that my Grandfather bought. My Uncle Bill had the other one. Trust Funds for the brothers, but not for my mother or her sister, they were expected to marry well. My aunt married into the Vanderbilt family, not my mother. Hence I’m the DIY bargain hunter.


elliottbnewcombjr
dekay's avatar
dekay
5,385 posts
 
Slow start rectifier tubes (like 5ar4) can also mess with reforming caps using a Variac.

A local guy pieced together a simple SS plug in rectifier to reform the caps in my Pilot 232.

I was in a hurry once and subbed a 5Y3 for a 5ar4 when reforming the caps in Dynaco IV's.

Anyway, if it's tube rectified research the rectifier tube.

DeKay
jea48
4,313 posts
 
Unless the amps were modified there are not any regulators in the amps. A schematic wiring diagram can be found in the instruction manual.

Just a guess the power supply caps were replaced as well as any coupling capacitors.

I would probably pull all the tubes except the 5V4 full wave rectifier tube and bring the amps up slowly using the VARIAC. That will, should, reform the electrolytic caps in the power supply, if needed. If no smoke reinstall the tubes and bring the amps up on Line again with the VARIAC .

If in doubt though you might try sending a PM to @atmasphere.
Or if you are lucky he might read this thread and respond.


totem395
390 posts
 
4 years isn't all that long ago but along with a Variac you
may want to look into adding a dim bulb tester.

 http://www.geek-tips.com/2015/11/22/dim-bulb-tester/
elliottbnewcombjr OP
5,239 posts
 
moisture is not an issue, they are in climate controlled basement, thus no humidity, never too hot or too cold.

no diodes in the parts list.

It has one 5V4G Rectifier Tube.

so, others out, 5V4G in, do the variac thing,

then other tubes in (one 12AU7; one 12AT7; Two EL34 (originals were EL-37) and repeat the variac thing.

I'll go test the tubes now.


fiesta75
1,378 posts
 
I agree with jea48 and totem395. Four years isn't very long really for new caps, I doubt you will have any problems. I have a variac and use it often on old equipment. For me, I wouldn't even use it for these Fishers if what you're saying is accurate. A slow voltage increase could create problems.
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