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How to repair and refurbish vintage tube amps?
How to repair and refurbish vintage tube amps?
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Old 10th April 2011, 01:25 PM   #1
analogadikt is offline analogadikt  India
diyAudio Member
Join Date: Jan 2011
Location: Mumbai, India
Default How to repair and refurbish vintage tube amps?

Hallo everybody,

I have a few vintage amps that need repair and refurbishment. I am a novice as far as valve circuitry is concerned, although I have been dabbling in DIY electronics since childhood. I shall be doing this myself as there are no professional experts in valve/tube technology available here. The old timers have closed shop, retired and gone away.

I am now preparing “how to go about this job” notes to guide me and request experienced members to help fill the gaps in my knowledge and provide answers. The equipment I have consists of hand tools, soldering guns, DMM and bulb tester with 15, 40 and 100 watt bulbs.

I am aware of the extreme caution to be taken while working on such equipment, because of the high ac and dc voltages in the equipment.

The procedure:-
1) Clean the amp chassis of accumulated dust, cobwebs, dead insects etc.
2) Clean all pots, switches, valve sockets, RCA terminals and speaker terminals with electronic grade contact cleaner (“safe with most plastics” type)
3) Connect speakers and slowly power up through the bulb variac.
4) If the high wattage bulb does not light up, or is dim, then connect directly to mains and check if the chassis is live. This check shall be done with one probe of the DMM on the chassis and the other connected to the earth on the wall outlet.
5) Replace the capacitors and resistors. Here, I seek advice on what types of caps and resistors are best.
6) Check voltages on valve pins and bias. I know heater should have ac current only, but what about the anode? I checked anode voltages for the first time last week and found both ac and dc current. Is this correct? Also, how to check bias? Any other method than this? Bias FAQ
7) Hopefully, the amp should work properly after this and is ready for minor upgrades such as replacement pilot lamp with LED (How do I do this?), in-rush current limiter, delayed start (something like this http://www.nervenet.info/HT_delay/ax_aug-2001.pdf ), individual bias pots on each tube (How is this done?)

There must be some dumb methods that I have contemplated, and have probably asked some dumber questions. Also I am asking for this advice on other forums too. I hope members here do not mind that and thank in advance for the valuable advice received from them.

With Best Regards,

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Old 10th April 2011, 01:51 PM   #2
LinuksGuru is offline LinuksGuru  Europe
diyAudio Member
Join Date: Aug 2008
Hi !

You can find a complete walk-through of restoration process in my blog:

Pioneer SM-83 Vacuum Tube Amplifier Restoration | MacGuru HQ
Fisher 400 Vacuum Tube/Valve Tuner/Amplifier Restoration | MacGuru HQ
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Old 13th April 2011, 03:39 PM   #3
analogadikt is offline analogadikt  India
diyAudio Member
Join Date: Jan 2011
Location: Mumbai, India
Originally Posted by LinuksGuru View Post
That is very helpful.

Thanks and Regards
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