Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: knotscott on November 20, 2012, 07:02:39 am

Title: Substituting pots
Post by: knotscott on November 20, 2012, 07:02:39 am

Hi gang - More than 2 years ago I started an 18 Watt Stout without the hotswitch, and have just recently pulled it out of mothballs to finish it. 

My question is can I substitute 1 meg pots in place of the 500K pots for volume and tone controls?  If so, any tweaks needed?

TIA!

Title: Re: Substituting pots
Post by: Jack_Hester on November 20, 2012, 07:23:53 am

You should get more resolution to your volume.  A finer adjustment.  On the tone, you should get the same change in resolution, but I can't say how it will affect the sound.  I'm hoping someone will speak up and give you a better analysis.

Is this the schematic that you followed?:

http://www.el34world.com/projects/images/Hoffman%20Stout%2018watt%20No%20Switch%20Schematic.GIF (http://www.el34world.com/projects/images/Hoffman%20Stout%2018watt%20No%20Switch%20Schematic.GIF)

Jack

Title: Re: Substituting pots
Post by: Geezer on November 20, 2012, 07:26:28 am

Yes, those should work okay. However, if you find the controls are a bit funky, you could place a 1meg resistor across the outside lugs of the pots to replicate a 500k.

$0.02

Geezer

Title: Re: Substituting pots
Post by: knotscott on November 20, 2012, 08:07:56 am

Yep....that's the schematic I used.  Thanks to both of you.

Title: Re: Substituting pots
Post by: HotBluePlates on November 20, 2012, 08:04:31 pm

You can make those changes.

It change the range of frequency for the tone control. Best guess: you will like the tone circuit as-is. If you don't, and want original operation, halve both of the caps.

Increasing the pots to 1M will also slightly increase the gain of the input stage, due to reduced loading from the pots.