Vacuum Tube Extension Rig

[AlgoRhythms]

I have a pair of power amps that use a single 6SN7 type tube as the first gain stage, after the input. The tubes are mounted internally in a horizontal configuration, one per amp.

I want to replace the Soviet era tubes (6H8C ) with something more modern and higher quality 6SN7. The modern tubes are excellent but, aside for a couple of manufacturers, all use a
larger glass envelope, probably for aesthetic reasons.

My amps have a small space allocated for the tubes. Modern ones just won't fit.

My question is this:

Is there any reason why I can't make a vacuum tube extender and sit a new 6SN7 on top of the amp, just above the original tube socket? I imagine a male set of tube pins wired with short (8 in) of connecting wires to a female tube socket that sits just outside and above the original socket. The new tube inserted into the new female socket and the male end of the extender inserted into the original socket that resides inside the amp.

Can anyone find a problem with this?

Advice is appreciated.

Please don't suggest alternative tubes as that's not the question I'm interested in.

Thank you.

Michael MacDonald
AlgoRhythms Mastering

 

[radardoug]

Well, you dont want to be told to use a different tube, but... USE a DIFFERENT TUBE! The 12xxx7 series are all smaller tubes than a 6SN7, so use one of those.

 

[AlgoRhythms]

Well, you dont want to be told to use a different tube, but... USE a DIFFERENT TUBE! The 12xxx7 series are all smaller tubes than a 6SN7, so use one of those.

That's an avenue I'm investigating independently. I'm looking for responses as to possible problems with my proposed extension and not suggestions about tube selection.

 

[rock soderstrom]

Are the existing sockets mounted on PCBs?

I think your idea might work, though extra long cables and additional adapters can cause problems due to their extra capacitance/resistance, maybe it would be better to wire the new tube sockets directly. Any gridstoppers should be mounted directly to the new sockets, although the 6SN7 is not particular susceptible for oszillation. Your are dealing with line signals here. Keep inputs and outputs separate! AC or DC heater?

 

[AlgoRhythms]

Thanks for your answer.

The sockets are mounted on PCBs.

Changing the tube sockets doesn't solve the problem. It's a real estate issue. Modern 6SN7 tobes seem to love a vintage, larger style of glass envelope. The very best ones are using a globe shape.

I don't know if they're headed AC or DC. How would that make a difference?

The block diagram I have isn't very detailed. And a schematic isn't available.

I've seen rigid extensions made, to make a tube stand taller, but never an extender with flexible wiring.

 

[Disco Volante]

Just out of curiosity I'd like to see a picture of the situation?
I concur with rock that you might see instability due to higher capacitances.
Some amps have lowered their output tubes on a small shelf into the frame, but I guess that's not where you're at.
And I guess the point is to be able to use new production tubes, so NOS is a no-no...

Try it, see what happens, report back, we'll all be wiser?
Happy tinkering
V!

 

[rock soderstrom]

The sockets are mounted on PCBs.

Changing the tube sockets doesn't solve the problem. It's a real estate issue. Modern 6SN7 tobes seem to love a vintage, larger style of glass envelope. The very best ones are using a globe shape.

I had meant it differently, the cleanest solution would have been to replace the old sockets with the new ones on the enclosure, that would have avoided the adapter and you could have attached the relevant components closer to the new sockets. Unfortunately, this is not as easy with PCB-based circuits as it is with P2P or turret board designs.

I don't know if they're headed AC or DC. How would that make a difference?

Well, 20cm more supply lines for the heater are easier to realize with DC than AC. It works, but you quickly run into hum problems, if you are not careful enough. That's why

Photos available?

 

[AlgoRhythms]

Here's an image looking straight down on the tube. It's the first stage gain. As you can see, the tube is mounted horizontally with just enough head space to insert or remove.

Sure, but would the higher capacitance be sufficient enough to alter performance?

Yes, there are some fantastic new 6SN7, extremely low noise, extremely low microphonics and very well balanced halfs.

I might give it a try but want to be sure that the idea isn't foolish.

Thanks again

Michael

 

[rock soderstrom]

You could lower these PCB stand offs this would give you more headroom for the 6SN7 but I guess it would be not enough for all types...

Sure, but would the higher capacitance be sufficient enough to alter performance?

You won't know until you try it out. There may be problems, but if you do it carefully, it should work.

Edit: I guess the 6SN7 is DC heated, but I am not 100% sure. Check this regulator with the cooler. What type is it?

 

[AlgoRhythms]

Actually, lowering the standoffs might work. I have to measure to see how much space that would add. And I would have to use some sort of a standoff though.

But that might be a better solution to the tube extension idea.

Thanks.

Michael

 

[AlgoRhythms]

But I'm still interested if the tube extension would work.

 

[rock soderstrom]

You know my opinion, but I can't guarantee success. My damn crystal ball broke yesterday.

 

[AlgoRhythms]

Indeed, and I thank you for it.

I'm looking for advice, not validation.

 

[Rusan]

It's hard to tell from the photo, but do you have have room behind the tube for it to fit at 90° to the plane it's situated in now? You could try making a right-angle adapter from a 90° PVC or ABS pipe fitting with a blank octal tube base at one end and an octal socket at the other. That way, you'd have very short jumper wires, no modifications to your amps, and if you found it was necessary you could easily shield the adapters with copper foil tape.

You could even make a similar adapter with a noval socket, which would allow you to use 6CG7/6FQ7, the 9-pin 6SN7 equivalent. Very good NOS is available for less than $50, if you ever did decide to go the old stock route. Or, a loctal socket, which would allow for use of the 7N7, a loctal base 6SN7 that costs less then $20 for good NOS.

 

[AlgoRhythms]

It's hard to tell from the photo, but do you have have room behind the tube for it to fit at 90° to the plane it's situated in now? You could try making a right-angle adapter from a 90° PVC or ABS pipe fitting with a blank octal tube base at one end and an octal socket at the other. That way, you'd have very short jumper wires, no modifications to your amps, and if you found it was necessary you could easily shield the adapters with copper foil tape.

You could even make a similar adapter with a noval socket, which would allow you to use 6CG7/6FQ7, the 9-pin 6SN7 equivalent. Very good NOS is available for less than $50, if you ever did decide to go the old stock route. Or, a loctal socket, which would allow for use of the 7N7, a loctal base 6SN7 that costs less then $20 for good NOS.

Interesting ideas. I'll investigate how much space I have. I could try other tubes but I found a new 6SN7 which is exceptional, so I'd like to try that if I can get it to fit.

 

[Cqwet Dbdfte]

Looks OK, 6SN7 is a great tube, I see no reason to change it.

 

[frans]

Most of my best tubes in preamps or mics are soviet military spec types, i'd first see if i'd get one of the original tubes NOS.

 

[AlgoRhythms]

After reading the comments here and doing a lot more research, I've decided that the vacuum tube extension idea is a bad one. The advantages of using a modern, premium 6SN7 tube are outweighed by the multiple problems that could occur from such an arrangement.

Thanks everyone for your input. It's greatly appreciated.

Michael
AlgoRhythms Mastering

 

[terry setter]

The photo looks like there might be room for a real, NOS 6SN7 in there as it is. I'[m sure you must have considered that, but, if not...

Many other good driver tubes to choose from, and many have been mentioned already. I happen to like the 12BH7 quite a lot.

 

[Wavelength]

I have a pair of power amps that use a single 6SN7 type tube as the first gain stage, after the input. The tubes are mounted internally in a horizontal configuration, one per amp.

I want to replace the Soviet era tubes (6H8C ) with something more modern and higher quality 6SN7. The modern tubes are excellent but, aside for a couple of manufacturers, all use a
larger glass envelope, probably for aesthetic reasons.

My amps have a small space allocated for the tubes. Modern ones just won't fit.

My question is this:

Is there any reason why I can't make a vacuum tube extender and sit a new 6SN7 on top of the amp, just above the original tube socket? I imagine a male set of tube pins wired with short (8 in) of connecting wires to a female tube socket that sits just outside and above the original socket. The new tube inserted into the new female socket and the male end of the extender inserted into the original socket that resides inside the amp.

Can anyone find a problem with this?

Advice is appreciated.

Please don't suggest alternative tubes as that's not the question I'm interested in.

Thank you.

Michael MacDonald
AlgoRhythms Mastering

Why not some nice NOS ones. Grab soe Sylvania 6SN7WGT super nice!