Tube amp bring up after 20 years in storage

[WOPL Sniffer]

I had a local gent contact me asking if I would give him some assistance with 2 Linear Acrosound tube amps circa 1950 that have been in a box for the last 20 years. I have a question for you tube geeks out there. I have heard of tube amps that were acting stupid/blowing smoke because they didn't like being fired up without any load on the speaker terminals and I was wanting to know what you guys thought of bringing up these amps with the load bank disconnected or attached to the speaker terminals with a Variac for the power source. I asked him if it needed to be loaded and he said "Good Question, I don't know". I'll give them a good lookover before we apply power. for safety sake. 20 years of inactivity on a set of 70 year old tube amps is probably iffy but you never know. I could also pull out the tube tester but I don't know if it is operational at the moment. I had planned on trying to restore it but don't have the time right now. THOUGHTS????

 

[mr_rye89]

I've never brought up a tube amp without speakers attached so I don't know if the output trannys will blow up. I've had my 300B amp on without speakers attached momentarily and nothing happened. The caps you can see don't look that old but might reform a bit if power is applied.

TL;DR attach load while bringing up just to be safe.

And what the hell are those output tubes and what's the deal with that perf board?

 

[WOPL Sniffer]

I've never brought up a tube amp without speakers attached so I don't know if the output trannys will blow up. I've had my 300B amp on without speakers attached momentarily and nothing happened. The caps you can see don't look that old but might reform a bit if power is applied.

TL;DR attach load while bringing up just to be safe.

And what the hell are those output tubes and what's the deal with that perf board?

I think they were kits you could build.

TLR????

 

[mr_rye89]

I think they were kits you could build.

TLR????

Too Long; Didn't Read

And octal tubes with the pinched off part at the top is weird.

 

[Skratch]

I use resistors for the load when bringing up old tubers

 

[WOPL Sniffer]

I use resistors for the load when bringing up old tubers

Yeah?? You just grab some 1/4 watt 10 ohmers leftover from a wopl build????

 

[krellmk]

Pull output tubes and do a voltage check all around without speakers

 

[MB1953]

Hi WOPL Sniffer;

In the past I have used a variac to bring up my old tube equipment, with load resistors on power amps.

More recently, built and use a light bulb tester for same purpose, using a 150 watt 3way incandescent in stages with switchable bypass option.

A web search can provide examples and explanations:
https://www.diyaudioprojects.com/Forum/viewtopic.php?f=5&t=1051&start=20

Also, use load resistors when the condition of the amp is unknown.
(concern about "blowing Up" from no load is eliminated)

Speakers after all is good.


MB

 

[BlueCrab]

Definitely do not turn them on without a load on the output transformers.

 

[BlueCrab]

Tube amps will generally survive momentary (short term measured in seconds if not minutes) disconnects of the output load, but it stress the output transformers and output tubes. With no audio input the load resistors need not be high wattage.

My recommendation would be to check the output tubes cathode current (probably easiest done by measuring the cathode voltage - generally there is a cathode resistor - just measure across it and divide by its resistance) as you bring up the voltage on the variac. This will ensure that none of the output tubes are running away and pulling so much current that it puts the output transformer at risk.

 

[WOPL Sniffer]

Tube amps will generally survive momentary (short term measured in seconds if not minutes) disconnects of the output load, but it stress the output transformers and output tubes. With no audio input the load resistors need not be high wattage.

My recommendation would be to check the output tubes cathode current (probably easiest done by measuring the cathode voltage - generally there is a cathode resistor - just measure across it and divide by its resistance) as you bring up the voltage on the variac. This will ensure that none of the output tubes are running away and pulling so much current that it puts the output transformer at risk.

Cool, thats what I figured. I have James Bongiorno's ( Marantz, Dynaco, SAE, SUMO Electric, Great American Sound Company (GAS) Ampzilla, Constellation Audio ) Load Bank rated at 1000Watts so I'm good.

 

[WOPL Sniffer]

The load bank has resistors the size of a turkey leg

 

[BlueCrab]

Looking at the photo it looks like it has been updated sometime in the past - the perf board doesn't look original. If this is the Acrosound Model Ultra-Linear II, then the cathode resistors are R17 & R20 using the schematic from Radio Museum. Output tubes are EL34s and the cathode voltage should be around +3VDC. Hope this is the model.

 

[BlueCrab]

The load bank has resistors the size of a turkey leg

Ha ha. That should suffice.

 

[WOPL Sniffer]

Looking at the photo it looks like it has been updated sometime in the past - the perf board doesn't look original. If this is the Acrosound Model Ultra-Linear II, then the cathode resistors are R17 & R20 using the schematic from Radio Museum. Output tubes are EL34s and the cathode voltage should be around +3VDC. Hope this is the model.

Can you post the link the skizmo? I had to actually go figure out what he had since he told me it was an Acrosoud.... I though it was an Iranian amp made of sticks and camel shit then I figured out he misspelled it so I won't really know till I see it in the flesh.

 

[J!m]

Perhaps add a real turkey leg amongst the analogues and heat 'er up.

 

[WOPL Sniffer]

I like the big rig exhaust stack by the 34's

 

[BlueCrab]

Acrosound Ultra-Linear II

Here's the link & the schematic is attached.

 

[BlueCrab]

Is that the one?

 

[WOPL Sniffer]

Is that the one?

I'll know soon enough. I had to ask the guy to verify what the hell he has..... He said it was a "Linear Acrosoud" which there is no such thing. I'm just going to power them up for him to ensure they are "Functional" for him to deal with. I'm not taking on any jobs this year until I get all MY project fingered out. Thanks