Triode Pentode Switch - Details

[diddymix]

Hi Folks,

I was hoping someone could help me I'm trying to do the triode pentode switch on the 4 x EL84's on my marshall combo... I just have a question regarding the switch itself and the wiring of it. With the switch on ebay I've found many DPDT switches but they are all rated at 240VAC... but the switch will have over 300V DC going through it... is this a problem or is it not as simple as that? Also do I have to use a plastic switch just incase something shorts inside and the knob itself became live??

With the wiring I got someone to draw me a diagram on here a month ago.. but I never clarified with him..Ive attahced it here. It looks as though he's cut the B+ usual supply to the screen resistors, and then have them supplied through the switch in pentode mode. However in triode mode I cannot see how the screen gride would receive B+ power, all I can see is that they are connected to the plates and output transformer?? Am I missing something? Do the EL84's not require high voltage DC when triode connected?

Many thanks for your time!

[sluckey]

You just asked that exact same question yesterday. The answer is still the same.

[diddymix]

Sorry bud, its you again. Wanted a second opinion on that, hope you understand

[martin manning]

Your question was answered already in the other thread. The screens are tied to the plates, so they will have plate voltage on them (a few volts less than the OT CT at idle), and yes you are interpreting the schematic correctly. In triode mode the screen voltage follows the plate when signal is applied, as if it weren’t there.

A 250VAC switch should be fine (note the rating is in volts and amps), but I would switch the amp into standby before changing from one mode to the other. The insulation (dielectric strength) between the lever and the contacts should be much higher than that, and in any case if you are in standby it’s not a problem. Look at the rating on your standby switch ;^)

[diddymix]

Hi Martin. yes I'm aware that my question was answered in the other thread. I wanted a second opinion so I have full peace of mind before attempting this as I have limited understanding of valve circuits. Hope you can understand that. Thanks for the info

[pompeiisneaks]

Sorry bud, its you again. Wanted a second opinion on that, hope you understand

I hope you understand that sluckey has an amazing depth of experience. It's like going to the dentist with a cavity and telling him you want a second opinion because he says you need a filling.

If you need a second opinion on that... I'm lost.

~Phil

[diddymix]

Sorry bud, its you again. Wanted a second opinion on that, hope you understand

I hope you understand that sluckey has an amazing depth of experience. It's like going to the dentist with a cavity and telling him you want a second opinion because he says you need a filling.

If you need a second opinion on that... I'm lost.

~Phil

I didnt understand till now Phil but thanks for that, how was I supposed to know hes a qualified dentist? If youre lost on the fact that I might have not known that, it's a shame.

[pompeiisneaks]

Sorry bud, its you again. Wanted a second opinion on that, hope you understand

I hope you understand that sluckey has an amazing depth of experience. It's like going to the dentist with a cavity and telling him you want a second opinion because he says you need a filling.

If you need a second opinion on that... I'm lost.

~Phil

I didnt understand till now Phil but thanks for that, how was I supposed to know hes a qualified dentist? If you're lost on the fact that I might have not known that, it's a shame.

I'm not lost on the fact that someone may not know how well someone knows what they're talking about, but double posting, and being dismissive of others on a forum you're new on is not generally considered 'in good form'.

You can, on the other hand, in the same place you asked the question, just ask if anyone sees any problems with Sluckey's suggestion, instead of the double posting.

You can, also go read the forums and see that

a: he's been a forum member for a LONG time
b: he's got almost 1000 posts here,
c: read his hundreds of other fixes for people on the same forum to ascertain how valuable his information is.

This last one is part of what forums are about. Get information first, and then if it's not clear, ask people for clarification, not ask first and then keep asking to see if you get different answers.

Just asking two times in separate threads, if you weren't aware, is generally considered odd if not outside the norm. This is the core of sluckeys statement:

You just asked that exact same question yesterday. The answer is still the same.

~Phil

[Tony Bones]

Many more opinions are available via google. In fact, if you had done that first you wouldn't need to ask the question at all...

[Reeltarded]

haha

hahahahaha

hah

heh

heh...

[sluckey]

It's OK diddy. I'll just stay out of your threads.

[M Fowler]

Oh boy another newby craps all over himself!