6211 vs 12at7 vs ?

[Jcricket]

Hey folks, Just finished rebuilding a tube amp and putting the finishing touches on it. My sincerest thanks to Scuzzer - a lifesaver on this amp. He helped me install a couple of chokes and fix a few wiring problems with it.

This amp uses four 6v6gt outputs, two 6211 and a 5u4gb rectifier.

It sounds v e r y nice. Very smooth and articulate. However, I do wish it had a just a little more bass. I think it is possible taht the opt may be just a little small to do what I want.

Question, could I try rolling some tubes in place of the 6211???

I found this on the 6211 in a google search.

A less common vacuum tube, this is a class A amplifier twin triode with medium mu; lower gain than the typical 12AT7, even lower than even the 5965 (see below). It usually has larger, flat plates with diamond shaped points at the corners bent inwards. This construction adds rigidity to the plate structure. This vacuum tube is slightly lower in plate voltage and current ratings, but is still very usable in hi-fi stereos.Often used in preamp circuits with lower gain, lower microphonics, and mellow sound. Somewhat uncommon but this medium-mu tube sounds very good in place of the standard 12AT7. Great for making the gain on a guitar amp more usable or eliminating harshness in your stereo system.

So it is a lower gain version of the 12at7. What about using a 12ax7?

Any thoughts?

Finally, does bolstering up the coupling caps help with bass response - I thought I read that somewhere once and haven't been able to refind it.

 

[audiodon]

You might want to verify the pinout. I've seen some triple mica black plate 6211s that would probably be fabulously linear in that circuit. I didn't know the AT7 was a plug-in replacement though. I have read up on it and you're resurrecting rusty knowledge so I'm hedging a bit.

If I were to try 12AX7s, which truly are different tubes that might overload the next stage, I'd keep my volume way low on the tryout.

 

[Jcricket]

If you have any info o nthose triple mica black plate I would LOVE to see it. I'll do some googling and see waht I can find out.

Thanks!

 

[Scuzzer]

Slow down there hoss! Although you've gotten it up and running you're jumping ahead a few steps with the tube rolling.

First we need to make sure the 6V6's are running at a reasonable dissipation, remember they were only loafing along at about 8.5W each when we tested it before adding the chokes. Once we get the circuit to a reasonable operating point we can check the bandwidth of your outputs and see where they roll off on the low end. It is quite possible that you're looking for bass that the original transformers can't provide.

What value are the 6V6 coupling caps that are in there now? We can look at changing them out if they're undersized.

 

[Jcricket]

Hey Gary,
Sorry, just a little excited. You have got to hear this thing. It is incredible now.

The coupling caps are .047uf.

I suspect your right about the OPT's being just too small.

 

[Scuzzer]

If you're dying to try some other tubes in place of the 6211's, I looked it up and they have the same pinout as the 12au7, 12ax7, 12at7 but the closest match would be a 12au7. I doubt you could hurt anything by trying the other tubes but remember that the gain is much higher with a 12at7 and 12ax7.

 

[becketma]

You might find this link interesting:
http://www.audiokarma.org/forums/showthread.php?t=153098

It shows .1uF coupling caps to the PP 6V6s.

I've had great luck changing old .1 and lower caps with .22uF and lower 600V Russian K40Y PIOs and FT-1 teflon--CHEAP on eBay, even with the mailing costs.

At one time I found some .05uF POIs, but at a lot lower voltage, that I sub for .047uF--seem to work fine.

Recently, I bought 4 different RCA 6AN8s, which my integrated uses instead of 12AT7, and discovered that one of them sounded a lot better than the others--it improved the pace and clarity compared to the others.

You might get more of what you want by trying different era, brands of the tube you are using.

From my point of view switching from the 6201 to another type of tube might put you in a position of simply just not linking the era and manufacturer of the 12AT7 you try.

Best
Bob

 

[dsndblm]

Can you post a schematic of the amp? I'm looking to build one with just the tube complement you described.

Thanks!!

 

[Jim McShane]

Question, could I try rolling some tubes in place of the 6211???

Sure, it's a common pinout, same as the 12A*7 types. In fact not too many years ago it was considered highly desirable to roll a 6211 in where a 12AU7 had been.

I found this on the 6211 in a google search.

A less common vacuum tube, this is a class A amplifier twin triode with medium mu; lower gain than the typical 12AT7, even lower than even the 5965 (see below).

Okay, agreed.

It usually has larger, flat plates with diamond shaped points at the corners bent inwards. This construction adds rigidity to the plate structure. This vacuum tube is slightly lower in plate voltage and current ratings, but is still very usable in hi-fi stereos.Often used in preamp circuits with lower gain, lower microphonics, and mellow sound.

Huh? The #1 problem with using a 6211 (or a 5965 for that matter) is most 6211 tubes are screamingly microphonic!

Any thoughts?

Be sure any 6211s you buy are tested specifically for microphonics! Then give them a try, you won't do any harm. Use a simple o-ring damper if you like.

Finally, does bolstering up the coupling caps help with bass response - I thought I read that somewhere once and haven't been able to refind it.

Maybe. It depends on a lot of things. But do be aware that sometimes the couplers were smaller to limit low frequency bandwidth. If the OPTs saturate due to strong low frequency content it's not pretty! And sometimes they were just smaller to save a few pennies of the cost of building the unit, or to use a value already in manufacturing's stock.