Just got these tubes for IIc+..

[RocketRick]

I posted in another board and dodger said to post here..I really hadn't noticed this board. Just been going to the Vintage amp board..

Whelp I got these tubes. Not sure how I know if one is better then another tho.

2-RCA 3-Mica Black plate 5751/ECC83

Test at 118/130, 120/130, on a EICO 667 Tube tester.min:60
========================================
2-Matched RCA 5751 tubes (lo mu 12AX7 ECC83):
black ridge plates, 2 mica spacers, extra support rods between mica spacers and halo ring getters at the tops. Tubes appear identical in construction!

Hickok TV-7B checked @ 42/41 39/44
========================================
2- Matched Pair premium plate 12AX7
Fully tested on a calibrated TV-7 conductance tester at 43/47 and 47/49 where 32 is good. Originally sold and labeled for the Sanborn Company.
========================================
2 NOS Mullard 12AT7WA CV4024(12AT7 ECC81)

These are the low noise CV4024 m8162 British Military version of the 12AT7, manufactured by Mullard in Mitchum, Great Britain, not the inferior Mullard re-issue tubes currently available!
Coded '654 R4D3' (Mullard Mitchum, 1984)
Pairs selected by factoring in both IP and Gm.
Gm tested at 3600/4500, 3900/4900. Min 2500, average new 3850 mho.
IP (plate current) 3.8/6.6, 4.1/6.4. Average new 3.7 ma.
Fully Tested on a Hickok 539C tester and guaranteed.
==========================================
Most gave some readings for the tubes but not sure what that means. I think the numbers mean the plate voltage but some of the numbers are large and some are small..Must be in millampearage or millvoltages and some must give the whole number..

Kinda confusing. Like what does low mu mean?

Guess I need a primer on tubes.

 

[RocketRick]

I thght this was the place to discuss tubes for amps. I was direected to this board from the vintage board..

What gives. plenty of lookers but no responses... :?:

 

[Old BF Shred]

Like what does low mu mean?

mu is transconductance; how well the tube "conducts" electrons from cathode to plate.
This basically, "roughly" translates to gain (but not the same thing). It is one way to test for relative gain between 2 samples of the same tube.
Also good for testing if a 12ax7 tube's 2 triodes (sections) are balanced...good to know if selecting a driver (PI; phase inverter) for the output tubes.

The real test is if you like the sound......I use vintage tubes myself. I have a small collection of Telefunken, RCA, Amperex and Sonotone 12ax7 and 12au7's. I like the Tele's best, though all of them are smoother sounding than the new production tubes I've tried (including Mesa's), IMO.

The tubes you listed are generally lower gain than most 12ax7 types (exc. maybe the Sanborn), but they may still sound awesome....have you tried 'em yet? Let your ears be your guide!
Good luck!

 

[RocketRick]

Thanks for the info Old BF. I'm gonna find some info on testing tubes on the net and learn more about it. Did you get a tester?

Haven't tried them out yet. hope to try A/B comparison playing the same things at the same settings. Replace in this order:

1st - as is

2nd - replace V1

3nd - replace V5

4th - replace outside power tubers with El34's.

Also, will try just the El34's and see what that does.

 

[Old BF Shred]

I don't own a tester...had one (one of the Hickok models) where I worked back in the '70's, but even back then, we knew that sometimes the best test is old fashioned substitution to see what works in a given circuit, esp. for an intermittent problem or subjective audible differences.

I think you'll find that V1 and output tubes make the greatest difference. After V1, go down the line...V2, 3, etc...The PI (driver...possibly V5 in your amp) needs to be healthy to provide enough drive and can certainly make a difference, too (12at7 has higher current rating and many folks like them in the driver so don't overlook trying one there, too). You're correct to do them one at a time, so you know what changes what. Let your ears decide. The differences will likely seem subtle, so take your time listening carefully (heck, that's half the fun! )
Then do what your ears tell you!
BTW, el 34's will have less bass output than 6l6, but with more midrange presence, so you may really like the combination!
Good luck!

 

[RocketRick]

Thanks again Old BF Shred..

 

[Old BF Shred]

No problemo....
Let us all know what your impressions are when you're done testing! 8)
Later!