Need help with tube test data - fast

[HugoR]

Hi,

Would like advice before buying tubes. I am about to buy 4 6AN8A pairs (2 pairs/brand) and asked triode matching datas from the dealer.

Circuit uses a pair of 6AN8s for gain/phase splitting and has bias adjustment for each channel as well as test points and trimmer pots for DC and AC balance of each channel.

Is triode matching important in these conditions?

Here's the test data from the Zenith, Rogers valves.
Data is Triode / Pentode, in uMhos, measured/tested on Stark 9-66 Mutual Transconductance test set.

Rogers
4900/4100
4900/4700
4650/4200
4850/4250
4250/3800
3400/4100

Zenith (USA)
3400/3600
4500/3800
5000/4100
3900/3700

Zenith (UK)
5100/4100
5000/4050
3900/3650
4550/3850
3400/3950

As you can see, "matching" sets of triode-pentode tubes in brands is difficult.

Thanks for any and all help.
HugoR

 

[SY]

If the triodes are used as a split load (like the Dyna circuit), matching them is not terribly important.

 

[HugoR]

The circuit is a three-stage feedback amp employing a common 6AN8 triodepentode as the voltage amp and phase inverter. The input signal is applied to the 6AN8 penthode grid, after being coupled through a 15000 ohm isolating resistor. The penthode acts as a voltage amp and DC-couples the signal to the grid of the triode phase inverter.

HugoR

 

[SY]

That sounds like the Dyna circuit. Are the plate and cathode resistors of the triode equal? If so, it's a split load, it's operating under nearly 100% feedback, and the matching is not critical.

 

[HugoR]

IIRC, plate and cathode resistors are equal to 27000 ohm, 1W.

 

[HugoR]

I am wrong.
Plate resistor are different. See the circuit bellow.
R7 = 27000 ohm
R9 = 39000 ohm

Thanks

 

[SY]

Without commenting that the guy who drew this schematic should be taken behind the barn and spanked with an axe, you left off the important bit- the triode phase splitter in question.

 

[HugoR]

SY,
I am sorry. Image was too big!
The link of the complete schema is bellow... Hope it will work.
I appreciate your help.
Hugor

An externally hosted image should be here but it was not working when we last tested it.

 

[HugoR]

Retrying with the link

An externally hosted image should be here but it was not working when we last tested it.

.

Don't know how to handle IMG If link doesn't work. Sorry.

Thanks alot.
H

 

[HugoR]

Wow! Works this way.

 

[anatech]

Hi Hugor,
SY is right, mostly does not matter much. There is feedback too so that will reduce the differences. I would match output sections.
I see there is a way of balancing the AC drive to the outputs. Won't matter much. What brand of 7591's are you going to use?

-Chris

 

[HugoR]

Hi anatech,

7591 are quart matched JJ current production tubes and I have heard that they sound very good. Also, JJ filiale is based in Canada and it is easier for me to buy here and therefore avoid custom fees.

Thanks
Best,
Hugo

 

[anatech]

Hi Hugo,
Sounds not too bad, EH are also good. Customs and duty are hidden in everything, but UPS charges for clearing are nuts. Use a brokerage for US shipments or clear them yourself. Don't let UPS get a hold of it, whatever you do!

-Chris

 

[HugoR]

anatech,
Thank you for the tip. I am always trying to find products and parts in Canada for the reason stated above. Now, I will widen my horizon.

Best,
Hugo

 

[ErikdeBest]

Don't know if it is of much help, but it seems mr mojo built the same amp a time ago. PRR gave him great assistance, maybe it van be helpfull for you to.

Here is one of the

threads
There are more - give a search for 7591 and mr mojo and you will find them

 

[HugoR]

Same amp for sure.
Hugo