Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on November 16, 2011, 08:48:25 pm

Title: good voltages, good tubes, bad tone.
Post by: Colas LeGrippa on November 16, 2011, 08:48:25 pm

Hi , I have built this preamp up to the master volume and I get harsh distortion although voltages all are good. The two last 50-50 caps were replaced by a single 10uF , 450V. but I don't think it is the issue. Shielded wires everywhere where needed.....good speakers, ( good guitar hey hey hey.... ).
I did not wired the lo input jack, instead I have put a 68k/68k signal voltage divider

Any idea welcome

regards

Title: Re: good voltages, good tubes, bad tone.
Post by: 3choplex on November 16, 2011, 08:55:32 pm

10uF, or 100uF?

Title: Re: good voltages, good tubes, bad tone.
Post by: Heinz on November 17, 2011, 01:54:31 am

I assume 100µF.

But nevertheless that also eliminates the 10k resistor between the two 50µF caps which provides filtering between the stages. Even though it does not affect dc voltages very much, it de-couples the B+ rails of the first/second and the tone stack stages. Dropping it could cause high frequency oscillation which may be responsible for the harsh distortion sound.

Title: Re: good voltages, good tubes, bad tone.
Post by: Colas LeGrippa on November 18, 2011, 10:54:05 am

my mistake, everything's fine now, thanks

Colas

Title: Re: good voltages, good tubes, bad tone.
Post by: stratele52 on November 18, 2011, 03:28:37 pm

When I read your title ; "good voltages, good tubes, bad tone"  I said to myself; this is half the amps on the market today .

Good to know you find . 

Title: Re: good voltages, good tubes, bad tone.
Post by: Colas LeGrippa on November 18, 2011, 03:40:41 pm

you're dam right !

Title: Re: good voltages, good tubes, bad tone.
Post by: phsyconoodler on November 18, 2011, 04:56:32 pm

So,what was it?

Title: Re: good voltages, good tubes, bad tone.
Post by: Ritchie200 on November 18, 2011, 07:47:19 pm

When I saw this I thought it was Tubenit talking about his Tele again! :l2:

Jim

Title: Re: good voltages, good tubes, bad tone.
Post by: Colas LeGrippa on November 18, 2011, 09:01:19 pm

ooops sorry, I have miswired a 50/50 cap on the power rail, the schems are good, just my mistake.
Tone is marvelous now !
Colas

Title: Re: good voltages, good tubes, bad tone.
Post by: stratele52 on November 19, 2011, 04:47:28 am

Good news.

On a (re) built project almost all the problem is a mistake in wiring.