Ideally, a power meter, or at least an ammeter would be used with a variac, but the bulb is a passable workaround. Also as mentioned before, you should keep well below the recommended bias reading until the amp is fully powered, and has been on for some time. And yes, dummy resistors or speakers must be connected. Bad idea to run a tube amp with no load.
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.
- ...
- 15 posts total
thanks everyone, a good mix of input as always. and great sounding results! What I did: the 5v4 only: Variac 50V for 30m; 75v for 30m; 90v for 30m. then all tubes in, repeat. .................................. I tested the tubes, they are all good. They had quad matched EL34 (RCA’s made in Great Brittan), they are still matched in strength on the meter. They had original Mullard EL37’s when I inherited them, but eventually they got weak, and EL37’s cost too much way back then. I don’t need the extra power, many options exist. .................................... Before they were fed from my McIntosh SS C28 Preamp (or source direct). Now everything goes thru my McIntosh mx110z Tube Tuner/Preamp recently overhauled by Audio Classics. They are dead quiet together up to my max volume setting (as I hoped they would be/used to be with C28). One of the reasons I love the Cayin is because it sounds like these Fisher’s do (with added features and remote volume). Now, the Fisher’s sound like the Cayin. Hah. They are Hard Lookers. Donna says they look ’interesting’. they look like this pair of 80-AZ: I never had the metal cages, they were concealed in the console. https://reverb.com/item/40173234-pair-vintage-the-fisher-model-80-az-tube-amplifier-rare-military-ve... my Cayin looks one day old. https://6moons.com/audioreviews/cayin/a88t.html .......................................... thanks as always, you are a great bunch hear, Elliott |
One simple solution is to use an inrush current limiter. You just plug your amplifier into it and flip the switch. Maximum voltage is applied in about 15 seconds. I purchased mine at sigtomics.com, however I see that website is no longer active. The email address on my unit is tsiglin@sigtomics.com. hope this helps. |
I’m still perseverating on your basement with “zero” humidity. One important bit of advice that I and some others failed to convey is to always use a load resistance on the amplifier outputs. If you don’t have a suitable power resistor, you can use an old speaker or a single driver from an old speaker. But it sounds like you’re already up and running without any mishaps. |
- 15 posts total