I found this,
I consider it prudent but I think it is extremely correct
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.
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.
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- 15 posts total
In some tube amplifiers Zenor diodes are used to provide voltages to key elements of the circuit, for example the bias voltage on the grids of the output tubes. Diodes don’t conduct until a certain threshold voltage has been reached.Other kinds of regulatory tubes also are often employed. In such a circuit, it can actually be momentarily dangerous to the circuit when it is not supplied enough AC input voltage in order to activate these regulatory elements.Therefore, without seeing the schematic of your amplifiers, it is hard to give a yes or no kind of answer to your very specific question about the algorithm you outline. I personally would spend less time at the very low voltage settings. I would bring it up to 80 or 90 V within a few minutes, for example. Then go slow up to 120 V but that’s completely off the top of my head. If it was really overhauled within the last several years, you’re probably going to be OK anyway. |
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 |
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. |
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/ |
- 15 posts total