ideas for diy tube adapters?

[Chappy]

Hey, Chappy.

Thanks for the ideas. I had thought of making an adapter at some point that would let me measure voltages without opening up the chassis, but hadn't thought of the SS recitifier (although I have seen the product you refer to). Thanks for the idea.

As to the 6SL7 to 12AX7 converter, do you just have wires maping the octal pins to corresponding parts of the 9-pin socket?

Thanks!

Hi Rayandkerry

Yes that is exactly what I did for the converter. A short run of leads mapping from one set of pins to the other. Hardwired. All safely inside the clear plastic enclosure of the plastic relay cover. The only possible drawback to these covnverters is that they are about 1 3/4 tall. Not an issue for my homebuilt head but I guess they would look pretty ugly hanging upside down in a combo.

Chappy

[Chappy]

I've heard that the 6SL7 octal preamp is pretty similar to a 12ax7 and sound great.

However 12AT7s can generate some unpleasantly muddy sounding high-odd harmonics when overdriven (as I discovered), which hopefully 6SL7s wouldn't. And it is true that 6SL7s are said to have good tone. However, they can suffer from microphony issues and may need DC heaters.

I've heard these issues before about the 6SL7's but I have not experienced these problems personally. I made a head that uses 3 6SL7,s and it seems quiet enough to me. I have tried numerous used mil spec tubes in it and I haven't found one that is harmonic yet. I've also tried some NOS commercial tubes and they were fine too. I don't know, but maybe I just got lucky with what I have.

I actually built the 6SL7 to 12AX7 converter(s) to help me troubleshoot this amp. I wasn't happy with the overdriven sound and thought that maybe the octal tubes were the culprit. On intial experiments with the smaller bottles, I still get the ugly distortion so I don't think the 6SL7's are at fault.

When I get a chance (back home next month) I'll play with it some more and do some hum noise and distortion comparison tests and report back.

Cheers
Chappy

[rayandkerry]

Thanks, Chappy.

I think my first try will be the 12ax7 to 6SL7 adapter!

[Dana-L]

Here's an adapter I made which allows a 6AQ5 to be used in place of a 6BQ5:

-Dana

Looks pretty solid. Did you change the circuit too? The 6AQ5 is rated for 250V max and needs a different bias resistor. I know they're cheap, but you'd burn through them pretty quick in a 6BQ5 circuit.

I built this to run a 6AQ5 in a modded Valve Junior. The plate voltage in mine is about 360 and I've not seen any failures. I made no changes to the circuit; my adapter simply connects the like pins.

To answer another question, I ran a machine screw up through the bottom of the male 9-pin section and into the center metal piece of the 7-pin female section to hold everything together.

Cheers,

-Dana

[rayandkerry]

To answer another question, I ran a machine screw up through the bottom of the male 9-pin section and into the center metal piece of the 7-pin female section to hold everything together.

Cheers,

-Dana

Thanks, Dana. That was kind of the last open question I had on construction.

If I can get some time this weekend, I think I'll try and build an adapter so I can see what a 6SL7 sounds like in my SE amp (which takes a 12ax7).

Also, while I understand the many comments about the tubes not performing at their best unless they are in a circuit designed specifically for them, I am by no means a purist and really enjoy playing around.

I recently tried a 12ay7, 12at7 and 5751 in my SE amp and it sounded good in many cases. It all depends on the combination of pickups (single coil versus humbucker) and output tubes I am using too (6V6, 6L6, KT-66, EL34, etc.). The given amp just has a volume and a tone control (no master volume or VVR options). So swapping out the one preamp tube kind of allows me to fine-tune the relationship between pre-amp grind and power tube saturation/distortion.

Once I get my 18Watt up and running, I am sure I'll have fun listening to different substitutions in the first pre-amp position.

At any rate, it's all fun and I'm learning what I like and don't like every time I try something new.

So thanks for the tips everyone...I'll be using them soon!

Ray

[Dana-L]

Also, while I understand the many comments about the tubes not performing at their best unless they are in a circuit designed specifically for them, I am by no means a purist and really enjoy playing around.

Me, too.

A few years ago I scored a couple thousand used tubes on eBay and I've taken great joy in experimenting with "forbidden" substitutions. For example, I know from personal experience that subbing a 35CW5 for a 6BQ5 in my modded VJ sounds great and exhibits no reliability issues that I've seen. I'm sure it's not working in it's optimal range but it's good enough for rock & roll, baby!

Have fun!

-Dana

[dotfret]

And there's no 7-pin dual triodes.

There's the ECC91, and the Russian 6n15p (which is very similar).

Perhaps you meant that there's no interesting 7-pin dual triodes?

[krx]

And there's no 7-pin dual triodes.

There's the ECC91, and the Russian 6n15p (which is very similar).

Perhaps you meant that there's no interesting 7-pin dual triodes?

Righto. I wouldn't really call a common-cathode tube a true dual-triode.

[Shottky]

However 12AT7s can generate some unpleasantly muddy sounding high-odd harmonics when overdriven (as I discovered), which hopefully 6SL7s wouldn't.

I keep hearing about this, but I haven't actually *heard* it yet. If I were to design a proper Long-tailed PI with a 12AT7 in the 18W, would it be prone to producing these harmonics? Or would it require a higher-gain pre-amp?