Valve Junior Triode / Pentode switch

[grandmasterflash213]

Hi im looking to add a switch to my epiphone valve junior to go between triode and pentode mode on the output valve, after looking at schematics for various amps, it seems its quite easy, but can someone just verify that this idea will work?
Thanks!

[Tom Phillips]

John,

The topology you have shown in your mod drawing is commonly used in guitar amps for pentode/triode switching. However, it's better practice to put a 100 Ohm resistor in series with the screen when in the triode mode to prevent excss screen dissipation. Put the resistor in the red line between the plate and the switch. A one watt resistor should do.

Being a grandmaster, I thought you would know that

Regards,
Tom

[grandmasterflash213]

Ok thanks for that! I only know the basics of these things, just looked at loads of circuits of other amps and datasheets to compare.

Im a grandmaster of other things!

[davethehat]

how did you get on

have you done this mod yet?
i noticed that there is someone on ebay selling modded valve juniors with this mode including a standby switch so i presume he's using a a on/off/on switch.

http://cgi.ebay.co.uk/HOT-ROD-EPIPHO...QQcmdZViewItem

[Ruwaldo]

Same question, bigger amp...

I want to make the same mod to my Carvin Legacy. On the surface this seems like a simple mod to make but I'm sure there is more to consider than just throwing a resistor between two pins on each tube.

This is a scan of the power amp stage of the amp:




Can some of you super wise tube wizards look this over and give a newbie some input on making this mod?

Thanks in advance,

Russ

[Enzo]

Hi Russ, and welcome. Do us all a favor and start a new thread for your amp. We'll all see it, don't worry, and then we won't be hijacking grandmasters thread.

A standby switch on a Valve Junior? Oh please. Pretty soon we will be putting standby switches on the wah wah pedals. Maybe the drum kit needs one too.

[Ruwaldo]

Will do. Thanks for the reply.

[Steve A.]

Hi Russ, and welcome. Do us all a favor and start a new thread for your amp. We'll all see it, don't worry, and then we won't be hijacking grandmasters thread.

A standby switch on a Valve Junior? Oh please. Pretty soon we will be putting standby switches on the wah wah pedals. Maybe the drum kit needs one too.

Well, I was going to put a cooling fan on mine... LOL

If you checked out the link on ebay, the standby switch was incorporated into one of the other switches he had added to the amp (I forget which- darned BluesHeimers disease is effecting my memory! LOL)

My Epi Galaxie 10 came with a standby switch- which I removed and replaced with a "Texas Tea" style control to bypass the T-M-B tone stack. I happened to have one of the progressive toggle switches from Dave West so I used that. I think it is convenient to have a standby switch if it doesn't cost you an arm and a leg (or even an elbow and a knee!)

Steve Ahola

[Enzo]

Well if it makes you happy...

Flip a switch, turn a volume knob, seems about the same to me and the amp comes with a volume knob already. But I am old and grumpy.