Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Whiskeyzipper on April 11, 2016, 03:46:37 pm

Title: Blues Junior Conversion using 6V6 tubes (Component Changes)
Post by: Whiskeyzipper on April 11, 2016, 03:46:37 pm

Hello,

I’m thinking about ordering all the parts from Hoffman Amps to do the Blues Junior Conversion project to my Blues Junior amp to get rid of the circuit board.  I’m wondering has anyone did this conversion project and used 6V6 power tubes instead of the EL84 power tubes?   If so I wondered if anyone has marked up the Hoffman Blues Junior Conversion diagram to show what (if any) component changes need to be made? 

http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf (http://el34world.com/Hoffman/files/Hoffman_BluesJunior.pdf)

Obviously 6V6 tube sockets need to be used and cutting the tube mounting board so the 6V6’s can mount directly to the chassis is necessary but I was wondering if there are any resistors or capacitors that need to be different in the layout so I can order all the correct parts in one shot.  I was going to use the stock power transformer as I have read that it will work fine with 6V6’s and I have an upgraded TO20 output transformer from Heyboer I’m planning on using.

Thanks in advance for any input anyone can offer.   

Title: Re: Blues Junior Conversion using 6V6 tubes (Component Changes)
Post by: sluckey on April 11, 2016, 04:13:48 pm

You'll need more negative bias voltage for 6V6s. The BJ bias winding can't get there. So, copy the JCM900 bias circuit from page 5 of this pdf...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf)

Title: Re: Blues Junior Conversion using 6V6 tubes (Component Changes)
Post by: tubenit on April 11, 2016, 05:19:54 pm

You could change over to cathode biased 6V6's for a simple approach?  Which is what I would personally do since I favor cathode biased amps.

With respect, Tubenit

Title: Re: Blues Junior Conversion using 6V6 tubes (Component Changes)
Post by: Whiskeyzipper on April 18, 2016, 10:09:25 pm

Thanks for the info.  I greatly appreciate it.