DIY Tube Amp Fix

Your Add Here! · 22nd November 2004

I recently picked up 2 HH Scott 299, EL 84-based, tube hi fi amps. The one that I was banking on to use stopped working after a few hours. The other one is noisey and may become a parts-car for the first. I'm considering delving into trying to fix the one that broke. I have limited experience but know how to solder and can read a schematic somewhat. One side of the amp stopped working and all the tubes on that side don't light up now.

Can someone recommend a first step in diagnosing the problem and more general advice on me getting involved in fixing this amp?

Thanks

Geoff_T · 22nd November 2004

Quote:

Originally posted by Your Add Here!
I recently picked up 2 HH Scott 299, EL 84-based, tube hi fi amps. The one that I was banking on to use stopped working after a few hours. The other one is noisey and may become a parts-car for the first. I'm considering delving into trying to fix the one that broke. I have limited experience but know how to solder and can read a schematic somewhat. One side of the amp stopped working and all the tubes on that side don't light up now.

Can someone recommend a first step in diagnosing the problem and more general advice on me getting involved in fixing this amp?

Thanks

Hi

First question must be.. what test equipment do you have?

If you have a digital multimeter you can check the voltage hitting the heaters on the non-lit side. Doesn't sound very good because most amps get their heater off a 6.3 volt winding on the transformer with a humdinger preset pot. If the heaters are dead it's indicative that you might have blown the input fuse (if it has one) and you can check voltages and resistances on the working one and compare with the non-working.

I would also suggest a web search for a diagram so that you aren't working blind, and you can pick up Heathkit tube testers on EBay pretty cheap.

Your Add Here! · 22nd November 2004

Thanks for the reply. I just contacted a guy I met at a yard sale a few weeks ago to buy some test equipment if he still has it. He had variacs, scopes, tube testers, etc.

The way my life is going I'm probably going to need this stuff more and more. Lately, it seems I can stop watches just by looking at them!

Pipedream · 26th November 2004

The HH Scott amplifier schematics are here:

http://hhscott.com/database/vhhs_00011.html

Good Luck

- I would leave the "parts car" alone until you feel better.

Marty Shields. · 7th December 2004

First get a good meter,up to 1000v DC, then, check the transformer output to see why you hav'nt got any filament voltage, the valve filaments are wired in paralell usually. need 6.3v ac .
There may be a problem with the transformer supply if theres no output.
When you sort out the power problem, check for leaky of shorted HT caps, the 20uf and 100uf electros. and replace the coupling capacitors .1uf I think, this will ensure a good sound, make sure you use high voltage, quality Items. you could also replace the .o2uf's as well to ensure good performance.
You probubly should test the 6bq5's for emission too.
Hope this helps,
Marty Shields, Martstone Amplifiers.

22nd November 2004	#1
Your Add Here! Gear maniac Joined: Aug 2002 Posts: 171 Thread Starter	DIY Tube Amp Fix I recently picked up 2 HH Scott 299, EL 84-based, tube hi fi amps. The one that I was banking on to use stopped working after a few hours. The other one is noisey and may become a parts-car for the first. I'm considering delving into trying to fix the one that broke. I have limited experience but know how to solder and can read a schematic somewhat. One side of the amp stopped working and all the tubes on that side don't light up now. Can someone recommend a first step in diagnosing the problem and more general advice on me getting involved in fixing this amp? Thanks

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26th November 2004	#4
Pipedream Gear interested Joined: Nov 2004 Location: Ashington Posts: 1	The HH Scott amplifier schematics are here: http://hhscott.com/database/vhhs_00011.html Good Luck - I would leave the "parts car" alone until you feel better.

7th December 2004	#5
Marty Shields. Gear Head Joined: Jan 2004 Location: Tasmania, Aus't Posts: 66	First get a good meter,up to 1000v DC, then, check the transformer output to see why you hav'nt got any filament voltage, the valve filaments are wired in paralell usually. need 6.3v ac . There may be a problem with the transformer supply if theres no output. When you sort out the power problem, check for leaky of shorted HT caps, the 20uf and 100uf electros. and replace the coupling capacitors .1uf I think, this will ensure a good sound, make sure you use high voltage, quality Items. you could also replace the .o2uf's as well to ensure good performance. You probubly should test the 6bq5's for emission too. Hope this helps, Marty Shields, Martstone Amplifiers.