Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bub on May 16, 2011, 09:59:51 am

Title: Paralleling inputs on a 5F6-A
Post by: Bub on May 16, 2011, 09:59:51 am

Hi Gent's

I would like to use a toggle switch to bridge both triodes. Standard 4 input jacks set up. I ran a jumper as in TUT 1, page 5-32, figure 5-43, just bridging both triodes with a switch, nothing but squeal. Can I run the Bright channel through the toggle so when it is on both grids are running off the Normal input jacks and I disconnect the Bright jacks? I guess I'm also wondering why the squeal.

Thanks for any help

Rob     

Title: Re: Paralleling inputs on a 5F6-A
Post by: Bub on May 16, 2011, 11:22:58 am

It works perfect.

Thanks


Rob

Title: Re: Paralleling inputs on a 5F6-A
Post by: rzenc on May 17, 2011, 09:31:55 am

I did it to my own 5E3 and it works.
With a simple SPST switch, you can solder the junction of 68K input resistors on switch tabs and run shielded cable to pins 2&7 on first preamp tube. When you engage switch, both grids will receive the same signal...

Hope this helps.
Best Regards,
Rzenc

Title: Re: Paralleling inputs on a 5F6-A
Post by: tubeswell on May 17, 2011, 03:58:03 pm

I have done a similar thing to a 5F6A circuit in one of my own amps. Except I don't have a switch, I just ditched two of the input jacks (went to one hi-lo set that goes to both grids together) and use the vol controls to mix the two.

Title: Re: Paralleling inputs on a 5F6-A
Post by: sluckey on May 18, 2011, 06:48:41 am

Quote

I did it to my own 5E3 and it works.
With a simple SPST switch, you can solder the junction of 68K input resistors on switch tabs and run shielded cable to pins 2&7 on first preamp tube. When you engage switch, both grids will receive the same signal...

That's true. But if you look at your circuit you'll see that only half the guiter signal gets to the grids when the switch is closed. Essentially the same as playing thru the LOW input jack. You'll need a SPDT switch to isolate one set of inputs when you parallel the grids in order to get the full guitar signal to the grids. Take a look...

Title: Re: Paralleling inputs on a 5F6-A
Post by: rzenc on May 19, 2011, 11:07:59 am

Quote from: sluckey on May 18, 2011, 06:48:41 am

Quote

I did it to my own 5E3 and it works.
With a simple SPST switch, you can solder the junction of 68K input resistors on switch tabs and run shielded cable to pins 2&7 on first preamp tube. When you engage switch, both grids will receive the same signal...

That's true. But if you look at your circuit you'll see that only half the guiter signal gets to the grids when the switch is closed. Essentially the same as playing thru the LOW input jack. You'll need a SPDT switch to isolate one set of inputs when you parallel the grids in order to get the full guitar signal to the grids. Take a look...

I will give it a try and report back.
Thanks!!!

Best Regards
Rzemc