6V6 to 6BM8 pentode socket conversion idea

[tubenit]

OK,  both the Tweed BluezMeister 5879 OD and the D'Mars ODS can put around 305 volts on the power tube plates using a 5Y3GT rectifier. These amps are using either 6V6 or 6L6's.

AND ............ I have four "left over" 6BM8 tubes. I really like the sound of 6BM8's but I don't want to build a 4th amp.  So, I thought ......... well maybe I can create an octal to noval conversion socket and plug in 6BM8's?  I will not change LTPI values at all.

So this is my thinking ..................  I would use one of Doug's 9 pins & mount it on a slightly oversized piece of his turret board.  Then I would expoxy the turret board & socket on top of the 8 pin tube socket.

I would expoxy the 9 pin socket & turret board AFTER wiring up the conversion as in the illustration.  I'll also create a "cap" attached by wire to hold the 6BM8 in place given this is going in a combo amp.

Then I could simply add a SPDT switch to change the power tube 10w resistor from 6V6
to 6BM8.  

So,  ........... IF this works OK ............ I can flip a switch and change out 6V6's to 6BM8's in the same amp for two completely different amp tones.  

My questions are:

1)  What epoxy would be temperature rated to handle the heat to keep the turret board
     material and socket in place?  (remember the wires from the 9 pin to 8 pin socket
     will also help with that issue)

2)  Would you anticipate any problems with oscillation issues trying this out?

3)  Anything else that one can see that I am missing or not thinking thru well on this
     new experiment?

With respect, Tubenit

[sluckey]

My questions are:

1)  What epoxy would be temperature rated to handle the heat to keep the turret board
     material and socket in place?  (remember the wires from the 9 pin to 8 pin socket
     will also help with that issue) J B Weld from automotive store. Good for constant 500°F. Good insulator. Easy to use.

2)  Would you anticipate any problems with oscillation issues trying this out? No.

3)  Anything else that one can see that I am missing or not thinking thru well on this
     new experiment? Look at some other 9-pin sockets. Use one that will not allow the epoxy to get inside the socket pins. I would use solid wire for internal connections. Make all connections to noval socket first, leaving sufficient length to form and poke thru the octal base pins. When the noval is positioned to suit solder wires poking thru the octal pins. Fill unused pins with solder. Test for shorts with ohm meter. When everything is good fill the octal base with JB Weld and trim excess wire leads. Give it several hours to cure.

[tubenit]

Sluckey,

THANKS so much for the info and the direction on attempting this.  I have some JB Weld and did not know it would be a good insulator.  Excellent info.

Hopefully will get this idea tried out in the next two weeks and let everyone know how it goes.   

I appreciate your help as always!

Best regards and with respect, Tubenit

[kagliostro]

Hi Tubenit

But what about the triode in the 6BM8 bottle ?

K

[tubenit]

But what about the triode in the 6BM8 bottle ?

Not used. Not needed for what I'm doing.

When I built the Little Wing (mini-Bassman) and the HoSo56 that used 6BM8's, I did use the triode for the LTPI.  It works.  However, I do prefer being able to use a variety of 12A_7's in the LTPI if I want to for different gain values.

with respect, Tubenit

[kagliostro]

Ah, OK

Franco

[Stankfut]

What?!?! An unused triode (or 2)? That's just unnatural!

[tubenit]

Update on this conversion.

Tubenit

[Stankfut]

Okay, dumb question, but what program do you use for drawings?

[tubenit]

Always ExpressSCH.  Then sometimes will save that to a bitmap & then I can convert it to a GIF & then I can make more changes with "PAINT". 

Tubenit

[tubenit]

I used a 7/8" drill set to drill a hole for Doug's socket 

9 pin Ceramic socket and shield #2

  in  turret/terminal board material.

Then I traced the 8 pin tube socket on the board material.  I used a dremel tool to cut close to the traced circle. Then I used a sanding belt to round off squared edges to make a reasonably looking circle.   I would recommend an overage of the board material to it hangs over the edge of the socket base by around 1/8".

I mounted the socket on the board material with very small screws and used the cut off wheel to remove excess bolt.  I then lined up pin 2 on the 9 pin socket with the pin 8 of the 8 pin socket base.  The screws were hitting on the edge of the 8 pin socket base, so I used the
dremel tool to cut a small space for the heads of the screws.  This was done to allow a fairly flush fit of the turret board material (with the 9 pin socket) on top of the 8 pin socket base.

This took about 30  minutes because I had to figure some stuff out.

With respect, Tubenit

[tubenit]

Then I soldered the wires on to the 9 pin socket.  I measure how far into the 8 pin socket base the wires were going to go and left some insulation on to help prevent shorts and wires touching.

After soldering wires,  I then pushed wires thru the holes in the pins of the 8 pin socket base.  After pushing the pins thru, I bent the wire ends over so that they wouldn't pull out.

I then pulled gently one wire at a time until the turret board was getting close to being flush with the top of the 8 pin socket base. 

I then checked for shorts and wires touching to make sure everything was OK.  And it was. Once I was sure it was OK,  I soldered the wires into the ends of the pins on the 8 pin socket.

With respect, Tubenit

[tubenit]

After soldering the wires on the ends of the pins of the 8 pin base,  I checked AGAIN for shorts or wires touching. Everything was fine.

I used a corn cob holder (with only one prong on it)  inserted into the 9 pin sockets as a way to measure continuity and shorts, touching wires etc ....................       ( I use this same corn cob holder to separate braided wire on shielded wiring).

I installed the tubes and the tube socket retaining clips and plugged them in the amp.  It should be noted that the solid core wires I used did a great job of keeping the turret board and 9 pin socket stable long enough to test them. 

The tubes went into the Tweed BluezMeister amp with a 275-0-275 PT  using a 5Y3GT for maybe 305 volts or so on the plates of the 6BM8 tubes.  I had not yet added the SPDT to have a larger 10w cathode resistor.  So the test was done using a 270 ohm 10w resistor that was used for the 6V6's.

I think the amp sounded really FABULOUS to me!  Great tone & sweet harmonics.  Very smooth sounding, IMO.

After testing to make sure they work,  I used JB Weld to expoxy/weld the turret board material (with 9 pin socket) to the top of the
8 pin socket base.

With respect, Tubenit
 

[tubenit]

I haven't added the spdt mini-toggle to switch between the 270 ohm 6V6's cathode resistor & the 330 ohm (?) resistor for the 6BM8.

So far,  the project has only taken about 1.5 hrs to convert an amp into a very different GREAT tone using parts that I got from Doug.

I used his solid core wire,  8 pin socket base,  9 pin socket (like for EL84's).  

So this is a very EASY project, that is quick to do,  that is inexpensive and has great tonal results, IMO.

I can try this out in the D'Mars ODS also using a 5Y3GT & plan to do so.  I'll report how that sounds also.

I'm very happy how this turned out!!!  

Will try to update this after playing the amp some more and perhaps recording some soundclips.   So far, I like the sound and tone of a Tweed BluezMeister that is only 7 watts using the 6BM8's.

With respect, Tubenit

[kagliostro]

What about to insert an added resistor (~60ohm) for the cathode inside the adapter ?

K

[tubenit]

What about to insert an added resistor (~60ohm) for the cathode inside the adapter ?

It would not fit. Not enough space.  And it would need at least a 5 watt resistor minimum.

I plan to use a 470R/10w or 390R/10w.

Tubenit

[kagliostro]

Yesterday night I didn't considered heat dissipation and space required

Franco

[tubenit]

Update. 

This worked out really well!  IF I could only have one type of power tube in this amp, it would be the 6V6.

Having said that, the 6BM8 adapter plug in is a VERY fun change in tone.  Probably the best ZZ Top type tone I've gotten out of an amp. Somewhat compressed.  Easy to get the Billy G  "squawk".  Little more grit and great sustain.  Sounds great and I enjoy it but it's not my favorite tone. 

Surprisingly, the clean with the 6BM8 is a beautiful tone and sounds very sweet musically, but it's not all that clean to be honest.  I'd describe the amp as  clean/OD  to  OD plus. 

All I have to do to switch tubes is switch a SPDT from one power tube cathode resistor/cap to the other one.  And change the rectifier from a 5V4 to a 5Y3GT  ............. and then change the 6V6's to 6BM8's.    *  compare schematics.

I think the 6V6 is more versatile but the 6BM8 is truly a lot of fun to play. And the 7 watts isn't as loud as the 12-14 watts of the 6V6.

With respect, Tubenit

[kagliostro]

I think the 6V6 is more versatile

So the next adapter will be for 6aq5  tubes ?  

Franco

[sluckey]

So the next adapter will be for 6aq5  tubes ?  

Yep. I used a flat washer rather than fiberglass board. The washer was almost a perfect fit inside the tube base. Just a very, very light touch on the bench grinder and it fit perfectly.

[tubenit]

Sluckey,

 

That looks like something done by someone who knows what he is doing!!  Great job. 

With respect, Tubenit

[sluckey]

Just following your lead buddy.

[Willabe]

There both good ideas and the work was done well on both also.

I have a couple on sets of 6AQ5's maybe I'll make a set of adaptors for them.

               Brad     

[kagliostro]

Ciao Jeff

I was thinking again about the insertion of the required  add on cathode resistor

and I remembered the Yellow Jackets, you can add a pipe in order to have all the room you

need for the resistor and other components if required

(drop voltage resistor (or zener diode), resistor to increase grid resistor value and so on)



if you require more room the pipe measure can be chosen as to fit the external measure of the socket

instead of the internal like in the Yellow Jackets, a bit of cyanoacrylate adhesive can be used to

block the pipe correctly on the socket, for this adapters may be it will be better to use 9 pin PCB sockets

instead of the standard 9 pin sockets

---

May be this way is also possible to convert a Fixed Bias amp in a Cathode Bias amp, for sure you can

manage this thing to have a pentode to triode converter, but this can be done also with smaller adapters

Ciao

Franco

[tubenit]

I drew up a conversion illustration for the 6V6 to 6AQ5 tube.  Sluckey, if you did that differently, feel free to edit this post.


Regarding the yellow jacket type idea.  I'm not sure how one can put a resistor inside that and change the cathode value from 270R to 130R?   If you want to post a drawing showing that,  I'd be interested in seeing it.   

The other part of this idea is that I have NOT heard favorable reviews of the reliability of yellow jackets so I'm not sure I'd want to head that direction.  I don't know if the reviews are accurate but they left me wondering about the reliability of yellow jackets?

I am not sure what type of pipe that is not metal would be suitable?  And I am not sure how one would attach the wire to keep the tube held in place.

With respect, Tubenit

[kagliostro]

change the cathode value from 270R to 130R?

Well, you are right, there is a trick  , look to the wire that exit from the socket of this Yellow Jacket



you can imagine the purpose  

About Yellow Jackets reiability I don't know much, about TAD Tone Bone

I know they can have problems because of not well done solder joints

but if you build something for you I think you pay attention to details.

TAD Tone Bone has the tube fixed to the socket using high temperature red silicone

Both Yellow Jackets and Tone Bone uses a plastic tube

look to the firs page of this pdf

http://www.yellowjacketstc.com/sites/default/files/yellow_jackets_detailed_information_6.pdf

here in Italy we have choice between plastic tube for hydraulic use or plastic tube for industrial electrical installations

(you can use also other plastic tubes of course)

but I think you can improve performances using a copper tube (used usually for hydraulic)

something like Weber do for his WZ34 SS rectifiers



this way you override the heat problems encountered with Yellow Jackets to which someone complains

for an easy way to mount the 9 pin socket you can use on the pipe upper side a copper calotte like this



Ciao

Franco

p.s.: This is what is inside a Tone Bone Pentode

[tubenit]

Excellent information!  Thanks,  Tubenit

[birt]

in a B15 i made i added a big rotary switch to switch output tube cathode resistors. the same switch also switches between tube and silicon rectifier for appropriate B+ voltages. this means i can use 6V6, 6L6, 6L6GT, EL34 and 6550. if i wanted an option for 9pin output tubes i would have added a second socket instead of an adapter. ofcourse this is only for DIY amps.