Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: sean_thornton on October 10, 2016, 11:47:15 am

Title: Blues Jr plus TOS
Post by: sean_thornton on October 10, 2016, 11:47:15 am

I'm just theorizing here but i wonder whether the OD section from the TOS could be combined with the Blues Jr turret board. There doesn't seem to be any reason why they couldn't be, I was just wondering if anybody else has played with this idea. A hoffman turretboard combining the two should be easy to make. Thoughts? Comments?

Title: Re: Blues Jr plus TOS
Post by: tubenit on October 10, 2016, 06:13:40 pm

The Blues Jr uses EL84 tubes which overdrive pretty easily already. 

The Blues Jr has 3 gain stages going into an LTPI.  The TOS and other Dumblish inspired ideas typically have 2 gain clean gain stages (not 3) prior to the OD stage.

The Blues Jr uses 47uf and 25uf cathode caps on the first two gain stages compared to 5uf or lower value on most Dumblish inspired ideas in the gain stages.

The TOS OD section with the 5879 tube has a pretty overdriven tone, IMO. 

I am concerned that adding the TOS OD gain stage after the Blues Jr 3 gain stages (with large cathode caps) into an LTPI feeding EL84 tubes would sound like a buzzy chainsaw and/or mud and not have a transparent tone at all. 

I personally would not attempt this.

With respect, Tubenit

Title: Re: Blues Jr plus TOS
Post by: sean_thornton on October 10, 2016, 06:47:43 pm

I noticed the difference in cathode caps, i always felt the Blues Jr's  were a little high anyway. As i said, i was just theorizing, it just seems that as good as the Blues Jr is it has a lot of scope for "improvements". It strikes me that it might make a decent "Mesa" type of amp with the right OD section.

I agree with everything you said, especially el84s being easily overdriven, a friend of mine uses 6bw6 valves in his, very different tonal quality, doesn't overdrive the same way.

Anyway, i might put this idea on my "maybe someday" shelf.

Thanks for your input Tubenit, always appreciated.

Title: Re: Blues Jr plus TOS
Post by: tubenit on October 10, 2016, 08:55:51 pm

You might be able to convert to a Tweed BluezMeister which would have less overdrive and only 4 gain stages.  Also note the lower value cathode caps. 

I think you might need a 12AY7 in the V1 position followed by a 5751 in V2 and maybe a 12AT7 in the LTPI to get the gain clear and smooth enough using EL84's?

There is a SCH schematic and layout for this on the #2 reply here:

http://el34world.com/Forum/index.php?topic=17870.0 (http://el34world.com/Forum/index.php?topic=17870.0)

With respect, Tubenit