Tube score!

[Jeff Haddad]

Found these recently:

perfect lettering:

Unfortunately, no Amperex 12ax7's though...
The Sylvania's have late 50's date codes.

 

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8)

 

[capnjuan]

... Unfortunately, no Amperex 12ax7's though..

Too bad; but if you send me $50, I'll take them off your hands .... :wink:

A couple of years ago, Qvart was concerned about some harshness in the tone of his JM4100 ... a very gainy amp. He took Walter's suggestion to try either a 12AT7 (amplification factor 60 v. 12AX7 of 100) or a 5751 (amplification factor 70) in the preamp. He did so and he stopped giving his amp the tone finger.

The RCA 12AX7; black plates or gray?

Congratulations ... a super-fine set of valves there.

 

[Jeff Haddad]

I had heard that 12AT7's weren't the best for a preamp stage, maybe a high quality one like this will make a difference.

The RCA is grey plates - looks like what's in some of my 60's/70's Fenders:

The Amperex at's are made in Germany, the 12au7 is stamped made in Holland:

I have a Traynor Dark Horse which uses a 12au7 for the low-power section for amplification, I'll try it there...

The RCA 5Y3GT has a bit of a loose glass, hope it hasn't affected the vacuum.

 

[Walter Broes]

I had heard that 12AT7's weren't the best for a preamp stage, maybe a high quality one like this will make a difference.

They're not indeed - 12AY7's or 5751's are a better choice if you want to tame your amp a little bit. I have NOS 5751's in the first preamp tube slot of my tweed Bandmaster clones.

Congrats on the tube score!

 

[capnjuan]

I had heard that 12AT7's weren't the best for a preamp stage, maybe a high quality one like this will make a difference.

Hi Jeff: All of the 12A_7 tubes - and the 5751 - are functionally the same [two triode sections in one bottle] and share the same pinout ... tube socket connections.

All things being equal, you can substitute any one of them for any other and the amp will still work ... maybe sound not as good, maybe sound better but the only differences are each's ability to withstand high voltage and their amplification factors - by how much the tube's sections increase the strength of the signal.

12AU7: Amplification Factor = 17-19.5.
12AU7 data sheet
12AY7: Amplification Factor = 40.
12AY7 data sheet
12AV7: Amplification Factor = 37-41.
12AV7 data sheet
12AT7: Amplification Factor = 60.
12AT7 data sheet
5751: Amplification Factor = 70.
5751 data sheet
12AX7: Amplification Factor = 100
12AX7 data sheet

The 12AY7 has a relatively low amplification factor of 40; they were commonly used back in the day for capacitor input/grid leak-bias preamps like early Fenders and Gibsons that produced a sort of 'squishy' thing. With modern cathode-biased preamps, a 12AY7 v. a 12AX7 will produce the most noticeable drop in gain / increase in headroom.

12AU7s were, and are still, used as 'worker bees'; reverb drive and phase inverters; built to withstand high plate voltage but where signal strength and tone were less of a concern.

The 12AT7 and 5751 differ only in their amplification factor; one is slightly higher than the other. Respectfully and in a blind A/B test, I doubt whether the difference in gain would be detectable. Instead a listener might think one 'sounded better' .. but that difference could easily have more to do with one tube's inherent tone quality than its gain/amplification factor.

But ... if you're still unhappy with the AT7s, my offer to take them off your hands is still good!

 

[Jeff Haddad]

I have enough Fenders to find places to use the at's, but thanks for the offer, I'll keep it in mind!

 

[bluesypicky]

I have enough Fenders to find places to use the at's, but thanks for the offer, I'll keep it in mind!

Hi Jeff,
Just got me a 79 silverface Deluxe (uploaded this with it earlier today: http://www.youtube.com/watch?v=GQh4-HEF ... er&list=UL) given your experience with tubes and old fender amps, what would you suggest I put in it?
I'd like to experiment a bit, but I must admit I am clueless on the techie side.

Thanks!

 

[Walter Broes]

All of the 12A_7 tubes - and the 5751 - are functionally the same [two triode sections in one bottle] and share the same pinout ... tube socket connections.

All things being equal, you can substitute any one of them for any other and the amp will still work ... maybe sound not as good, maybe sound better but the only differences are each's ability to withstand high voltage and their amplification factors - by how much the tube's sections increase the strength of the signal.

Hey John,
Really not trying to be the contrarian here, but two different techs have told me that yes, of course, your amp will work, and you won't hurt anything with a 12AT7 in a preamp tube slot, but that it just won't sound good, because it wasn't designed as a preamp tube.

And that's the part I managed to remember - because both gents went on for ten minutes explaining to me in technical terms how and why and what, and I didn't understand a single word - as you know, I don't know a Volt from a Watt - so I'm basically just repeating what they told me about it not working very well as a preamp tube...ahem.

 

[capnjuan]

Hey John, Really not trying to be the contrarian here, but two different techs have told me that yes, of course, your amp will work, and you won't hurt anything with a 12AT7 in a preamp tube slot, but that it just won't sound good, because it wasn't designed as a preamp tube.

And that's the part I managed to remember - because both gents went on for ten minutes explaining to me in technical terms how and why and what, and I didn't understand a single word - as you know, I don't know a Volt from a Watt - so I'm basically just repeating what they told me about it not working very well as a preamp tube...ahem.

...

 

[Jeff Haddad]

bp - my experience is more 'what's in the amp when I bought it'. I really haven't gotten so far as to try alot of different tubes, I've just tried to buy replacements when I find interesting ones.

Based on the tone in that clip you posted, I don't think you really need to change anything. Nice playing! What's in that DR now? What don't you like about how the amp sounds (if anything?) Or are you just looking to get spares?

EH makes decent 6v6's if you don't want to spring for NOS. If you're selective in where you put them, you can get a couple nice old stock 12ax7's for the amp. Just put 'em where they count - if you use the vibrato channel, v2 and v4; or v1 if you're using the normal channel. NOS 12at7's are plentiful and not too expensive (v3 reverb, and v6 phase inverter). v5 is the vibrato (trem) oscillator and you can use just about any 12ax7 there. That's a good place to use any lesser quality or noisy tubes - all it does is turn on and off, there's not really signal that goes through it if I'm not mistaken. These tube numbers are counted by looking at the back of the amp and counting from right to left beginning with v1. The "v" stands for valve (tube).

Others may chime in as to which brand of tube sounds best for various tones, etc.

 

[bluesypicky]

Thanks Jeff.
The tubes are branded Fender 6V6's "special design" if that means anything....
I was misled into thinking they were mismatched but I guess not hmmm? :roll:
I think I'll take your advice and hang on to what I got as is.
I'm still in the bonding stage, and I like it more every time I play it in fact, the only thing I wouldn't mind is to get a little bit more punch in the bass range, but it's probably got more to do with the speaker no? It looks like the original one, all it says is "Fender" and guess what?... "special design" :lol: Guess it's a special design amp all the way through!

Since you mentioned old fender amps, I thought I would ask if in your experience with them, there were tubes that stuck out more than other, but as my friend and neighbor Capnjuan already told me, you really know what it'll sound like after you slap the tubes in and play it. (maybe he knows what he's talking about after all?) :wink:

Thanks again!

Pascal

 

[Jeff Haddad]

I'll defer to capnjuan on any technical issues - he seems extremely knowledgeable. As far as speakers, if the original is in that amp, that would be a weak spot. I like an old (not reissue) Jensen C12N in my SFDR, or a Weber 12F150 (their C12N equivalent). You'll get plenty of low-end from either of those.

 

[capnjuan]

12AT7 v. 5751 v. 12AX7 v. Godzilla v. the Oakland Raiders ... for those registered, on the Gear Page, there's a lively thread on the topic/s. Several very bright guys including Mike of KCA tubes and others. For those who like the Classics Comics version:

- Some people don't like 12AT7s in V1 ... the first preamp stage
- Some people like 12AT7s in V1 ... the first preamp stage especially if it's a good one like a Mullard CV4024 (military version of the 12AT7)
- Some people think that experimenting and letting one's own ears decide is the best thing
- 37 people who viewed the thread also bought Lays BBQ potato chips.

 

[bluesypicky]

- Some people think that experimenting and letting one's own ears decide is the best thing

That's the road I'll take. And I'm very interested in your PM offer! :wink:

- 37 people who viewed the thread also bought Lays BBQ potato chips.

:lol: :lol: :lol:

 

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When I have time, I need to go through my tube stash. I have two or three 12(something)7s with a military four number I.d. I remember looking it up and seeing it had an amplification of 30 or 40 and sorted it to the "good" tube caddy.

 

[capnjuan]

... And I'm very interested in your PM offer!

We'll schedule something ... I'll bring the chips :wink:

 

[bluesypicky]

... And I'm very interested in your PM offer!

We'll schedule something ... I'll bring the chips :wink:

Music to my ears....