Classic 50 Power Tube Relocation

[plexi50]

I dont like how peavey and some other manufactures mount the tubes horizontally inside the chassis. So after a lot of thinking and planning i made my move. I reversed the heater fuse and 100R screen resistors to the opposite side of the board to have access to them after remounting the board. I punched out the chassis for the EL84 power tubes and relocated the power tube board on aluminum standoffs. Then i thought i might as well put in a pair of octal sockets for some 6V6 tubes as well. I left the preamp tubes mounted as they were stock.  I have to wire up the 6V6 tubes and switch for switching between the EL84 and 6V6 power tubes.  I love 6V6 tubes and in think it will be a great addition. The original reason was to get the El84 tubes vertical and mounted on the chassis. The fan works but pulls in a lot of dust.  I found large balls of dust bunnies on the amp boards,power switches and transformers when i first opened up the amp

The first pic is the stock amp before going manic

[Platefire]

hay Man! Your Birthdays over, time to get back to reality. Well on the other hand mod away. I love 6V6's too, should be a great alternative. Peavey never had it so good, nice work! Platefire

[eleventeen]

VERY interesting project! Nicely done!

[kagliostro]

NICE IDEA

that way you have fresher tubes & an option for a mix of tubes

I have to wire up the 6V6 tubes and switch for switching between the EL84 and 6V6 power tubes.

how do you think to switch between tubes ? (or you mean swap tubes ?)

the hole for octal tubes looks absolutely perfectly done, what did you used to make it ?

Kagliostro

[plexi50]

NICE IDEA

that way you have fresher tubes & an option for a mix of tubes

I have to wire up the 6V6 tubes and switch for switching between the EL84 and 6V6 power tubes.

how do you think to switch between tubes ? (or you mean swap tubes ?)

the hole for octal tubes looks absolutely perfectly done, what did you used to make it ?

Kagliostro

I had to make a template of the power board using a piece of thin cardboard. I used a wet rag to dampen the top of the tube sockets and then pressed onto cardboard leaving a perfect print of the socket pins holes and center point of the tubes
I am going to switch the plate voltage from one set of tubes to the other using a heavy switch i have. I dont want the plate voltage on all power tubes at the same time drawing too much current and altering the transformer B+ to low

[alerich]

Love it!  Saved the pics for future reference. I'd probably never switch it back to EL84 (not a fan). That's the one reason I have not pulled the trigger on any of the several Classic 50 heads that have shown up in recent months locally on Craigslist. Good prices but I am just not an EL84 kind of guy. I am glad that Peavey did the tubes in the 6505 the same way as this. The preamp tubes are mounted horizontally but the finals are top mounted. The final sockets are still PC mounted at the terminals but the sockets actually screw into the chassis. Much sturdier than the preamp board. I actually like the preamp board setup in the 6505 and the Classic 50, though. Much of the peripheral preamp circuitry is on that board and it is way easier to access to do mods/repairs that than to pull the main board. Especially in the 6505 - nine board mounted pots. The 6505+ is even worse.

Very nice work. I'll bet that amp sounds bitchin' running 6V6's. I prefer my Egnater Rebel 20 dialed over the 6V6 side.

[kagliostro]

I used a wet rag to dampen the top of the tube sockets and then pressed onto cardboard leaving a perfect print of the socket pins holes and center point of the tubes

Nice tick

I am going to switch the plate voltage from one set of tubes to the other using a heavy switch i have.

ok I can follow you, with the switch you swap B+ from a pair of el84 to a pair of 6v6

but what about filaments ? Does your PS has enough current for the two more tubes connected at the same time?

Kagliostro

[plexi50]

I used a wet rag to dampen the top of the tube sockets and then pressed onto cardboard leaving a perfect print of the socket pins holes and center point of the tubes

Nice tick

I am going to switch the plate voltage from one set of tubes to the other using a heavy switch i have.

ok I can follow you, with the switch you swap B+ from a pair of el84 to a pair of 6v6

but what about filaments ? Does your PS has enough current for the two more tubes connected at the same time?

Kagliostro

The heater filament voltage with all tubes light up is 6.0 VAC across pins 4&5.  It's close. I have to wire the plate switching tommorrow and will see what happens. I got the 6V6 cathode biasing finished today along with a few other wiring changes to make some space for the 4-8-16 ohm speaker jacks on the old power tube cover plate. Man im tired

[LooseChange]

To turn off the tubes.... Just lift the cathodes and the tubes will not draw any current. Except for the heaters. Are you sure the PT can handle the extra 900 ma's?

[kagliostro]

Yes, LooseChange is right, better to switch the low voltage cathodes than the high voltage plates

With a DPDT switch you can swap between a pair of el84 or a pair of 6v6

the unknown is if the PS can give the more current for the two added tubes

may be you must switch also heaters so when you connect a pair of 6v6 instead of a pair of el84 you save from the heater supply 620ma instead to have 900ma of higher consumption if the 6v6 tubes heaters are allways connected

Kagliostro

[plexi50]

To turn off the tubes.... Just lift the cathodes and the tubes will not draw any current. Except for the heaters. Are you sure the PT can handle the extra 900 ma's?

Im not sure Dan. Is there a way to determine the transformer rating other than known PT specs ? I dont know what i have been thinking the past week. I have built several amps from scratch before and have used a switch to lift the cathodes to turn each set of tubes on or off

[plexi50]

Yes, LooseChange is right, better to switch the low voltage cathodes than the high voltage plates

With a DPDT switch you can swap between a pair of el84 or a pair of 6v6

the unknown is if the PS can give the more current for the two added tubes

may be you must switch also heaters so when you connect a pair of 6v6 instead of a pair of el84 you save from the heater supply 620ma instead to have 900ma of higher consumption if the 6v6 tubes heaters are allways connected

Kagliostro

Ive been thinking of a way to also switch the filaments off and on the pairs of tubes but havent figure that out yet. The one thing i didnt want to do was to drill any holes in the face plate. And i dont want to comprimise the tone by having a PT that may not be capable of the supply needed. Flying blind is fun. NOT!

[LooseChange]

First figure Peavey is not going to spend a nickel more than they have to just to overrate a PT. Then go by the old fashioned method and see how much the heater voltage sags with all the tubes installed.

Ive been thinking of a way to also switch the filaments off and on the pairs of tubes but havent figure that out yet. The one thing i didnt want to do was to drill any holes in the face plate. And i dont want to comprimise the tone by having a PT that may not be capable of the supply needed. Flying blind is fun. NOT!

If this is gonna be your amp... Just try either setup. Pull the tubes for the setup you don't like.

It's all fun.

[kagliostro]

The one thing i didnt want to do was to drill any holes in the face plate.

have you considered to close a little portion of the big squared hole you have near the fuse in the back panel ?

the power tubes aren't more in that place so the hot air coming from preamp tubes will be much less than previously

which was your initial idea about placing the switch for swapping plates ?

a 3pdt switch will do the job with only one hole

Kagliostro

[jeff]

I think you want to lift the cathode of the unused set of power tubes. Easy SPDT.

Don't just switch the OT to one sets plates or the other. Pretty sure it's not good to have voltage on the screens and nothing connected to the plates.

Also four EL84s and two 6V6s don't use the same load. If the amp has a multi-tap OT, plug the speaker(s) into the next higher output when using 6V6s.

EX: if the stock amp uses a 8 ohm load with four EL84s plug the speaker into the 16 ohm tap when using the two 6V6s.

(maybe use a DPDT switch instead of a SPDT switch, one side switches taps the other connects cathodes)

[jeff]

I'm worried about the extra heater current. Wouldn't wanna blow the PT. What I would do is this: I'd pull two of the EL84s, plug the speaker into the next higher tap and use the switch to select two 6V6s or two EL84s(cathodes). If you're in a situation where you need four EL84s swap the speaker back put in the extra EL84s and take out the 6V6s.

[plexi50]

All good ideas and i thank you all for your input. It's all fun for sure. I relocated the plate supply as it was too close to the rear speaker output panel. I used my dremel to cut out the bracket that mounts and secures the rear panel where the power tubes used to be also securing the speaker out jacks. So far i think this has turned out real well. This is a great sounding amp with the El84's. I cant wait to hear the 6V6's. All that is left to do is wire the speaker common and put in that SPDT for the cathode lift's. I promise i wont be doing this again anytime in the near future. It's brain drain

[plexi50]

I have the 6V6 tubes wiring  completed. I have a serious squeel as soon as i flip the standby switch. The El84's sound great as usual. OT polarity on the 6V6 tubes is not the issue. It's maginfying glass time

[LooseChange]

Dam! Hate it when that happens.

[plexi50]

Figured out my problem. I could not use the cathode bias i was trying to use along with the fixed bias on the power board. Long story. What i need is a DPDT switch to lift the cathodes of the tubes to switch between them. Then use the other side of the DPDT switch and add a 10--20k resistor in series with the 33k bias resistor on the power board to bring the bias of the 6V6 tubes down about 3 ma. Other than that it is working wonderfully. The 6V6 tubes are unbelieveable. Fat and sweet sounding in this amp. Not muddy or breaking up too early. Has a nice full warm wood tone.  They breakup nicely. Im glad i did all this. The main point was to get the tubes out into the air and out from inside the chassis but it went far beyond that.  More pics tommorrow after i finish the DPDT switching

[DummyLoad]

cool concept and nice craftsmanship!

--DL

[kagliostro]

Then use the other side of the DPDT switch and add a 10--20k resistor in series with the 33k bias resistor on the power board to bring the bias of the 6V6 tubes down about 3 ma.

not able to figure it

why is necessary the switch in the bias path ? is not the same to add the resistor in the path feeding the 6v6 tubes without the use of a switch ?

I've difficulties if I don't see a schematic

please can you explain ?

Kagliostro

[plexi50]

Then use the other side of the DPDT switch and add a 10--20k resistor in series with the 33k bias resistor on the power board to bring the bias of the 6V6 tubes down about 3 ma.

not able to figure it

why is necessary the switch in the bias path ? is not the same to add the resistor in the path feeding the 6v6 tubes without the use of a switch ?

I've difficulties if I don't see a schematic

please can you explain ?

I scrapped the cathode biasing and used fixed biasing for both sets of tubes
Kagliostro

[kagliostro]

SORRY not able to follow the reason for which you used a switch in the bias path  

OK, you use the fixed bias for all the tubes

that way isn't enough to adapt the path of the bias supply that carry the voltage to the 6v6 tubes in accordance with them, without the necessity of a switch in that path ?

or you didn't have in the bias chain the 3PDT switch  and I misunderstand you ?? ??

Kagliostro

[plexi50]

kagliostro, Ever have a day when you cant spell CAT or you fumble and drop things all day long? Well i wired the bias up wrong and re did it the right way. I dont know why i wired it that way in the first place. I am getting very forgetfull latley at what i am doing. I hate that. The dual fixed bias's are wired to each set of the power tubes cathodes. The back of the fixed bias terminals is lifted from ground using the push switch i put in place of the Normal & Lead channel switch. Now where to put that switch? Sounds great!

[kagliostro]

SORRY 

I've no more job, I'm losing it this days, so I haven't no much more to do than fumble

may be this will be many more time for amps, but not in this days, I'm too nervous

Kagliostro

[Tom_Hull]

same here .. artist oil painter nothing sell for now .. like doing downers .trying to keep my brain up but no ups .  (8[) i even lost my wallet.can it get worse ..yes  ..violin please or screaming amp ...i have to laugh at myself

[plexi50]

I put the Channel switch back where it was and put a small SPDT switch in between the power switches to lift the cathodes and switch between the EL84 & 6V6 power tubes. I had barley just enoungh room between the switches. Finished* I love this amp