OK, One of the secrets is that the 12AX7 triode section was lifted from the 12AV6! Also available as 6 & 3. These were designed for radio use and had the demodulator diodes built into a high gain audio triode. The 3AV6 is dynamite for portable microphone preamps! Also they cost less than $4! And you can get them as NOS from the manufacturers who's 12AX7's you drool over.
What is with people cleaning out stock? Do they buy the tubes and sell them on ebay for a profit once demand is up?
I understand buying volume (I bought over 100 6P1P-EVs) as I some times do if I expect to make use of the tubes, but cleaning out a stock of a thousand or more looks crazy to me.
I understand buying volume (I bought over 100 6P1P-EVs) as I some times do if I expect to make use of the tubes, but cleaning out a stock of a thousand or more looks crazy to me.
I'm trying to have at least two different tubes that can be used in each position. I've got the first set working, and just ordered some tubes from ESRC so I can try another set soon.
It woudl be nice to have three different tubes that could be used in each position for flexability and to insure availability for a while. I realize that this is not possible with a lot of tubes.
It woudl be nice to have three different tubes that could be used in each position for flexability and to insure availability for a while. I realize that this is not possible with a lot of tubes.
Can I interest you in any 6cw4s? When Cinch closed out their nuvistor socket production one surplus place bought them all. I would buy 50 at a time for I think it was 37 cents each and sell then 5 at a time on eBay. Someone else finally bought all of them. But by that time the eBay price was dropping to under $2 ea.
No big secret there. It says so in the RCA tube manual. What the book doesn't say is that the 20EZ7 is a 12AX7 with a 20 volt heater. All the tube places I called said that they had 50 or less in stock.
there goes the existing 12AV6 stock!
ESRC has over 3000 in stock, good luck buying them all. There are dozens of tubes like this containing a high Mu triode and two diodes. They were designed for AM radios using the diodes for the detector and AVC and the triode for an audio amp. If you look hard enough you can find them cheap. $*#! It isn't hard at all, the 4AV6 is on ESRC's dollar list. The 4BQ7 makes a good $1 LTP too.
I just placed my third order in 10 days. They are only 200 miles away so I get the tubes the next day.
You have to be careful in drawing these comparisons. The 6AV6 isn't quite the same as half a 12AX7. For the 6AV6: Pd= 500mW; 12AX7: Pd= 1200mW.
There could be other differences as well. The 6SF5 is another one of those types that seem similar to the 12AX7, but it's not (attached). Even with a CCS plate load, the H2 estimate is hideous (and would only get worse with passive plate loading). This is even worse than the 12AV7, and I didn't think you could get much worse than that. You can definitely help the linearity of the 12AX7 with active plate loading, and a good many of the reports of sonic under performance of this type relate to plate loads that are way too small. Here, that's as good as it gets.
The 6SF5 was designed for use as a first preamp for AM BCB receivers, and that's a distinctly Lo-Fi application. About the only other use for this type would be in a guitar amp. You'd never want to see it in any design where sonic excellence is the design criterion.
Attachments
Just out of curiosity I looked into the 6AF11. The site: The Squirrel Monkey One Tube Guitar Amp shows an amp using this tube. Aside from the often commented terrible and dangerous power supply, looking at the datasheet for the tube, the biasing shown appears to me to be completely wrong. I agree with the 10K (or higher) OT, but everything else seems way off. I have also read that this tube exhibits uncontrollable internal oscillations when used in this application.
He may have a transformer with separated line voltage windings. I have a couple like that, there is a barrier between the two.
He has the pentode biased a little hot but that may be to get the right tone. The triodes are not as gainy as they could, be probably to control the internal oscillations.
I would redesign the power supply using a conventional transformer. Does it make sense to use 200V for the triodes, around 47-68K for the plate resistor, somewhere around 1K - 1.5K for the cathode? 100K for the plate looks like it puts the operation close to cutoff.
6AV6 / 6AT6 were used in V1 on the mid 50's - early 60's Fender Tweed Harvard. Good bad or indifferent, in that application they sound amazing!
I have a box of Mint NOS 12AV7's (various brands) that I bought to try out, in the V1 spot of most amps I tried they were insanely microphonic. They might be good elsewhere, but I have never bothered trying them again since I still remember the squeal like it was yesterday
I have a box of Mint NOS 12AV7's (various brands) that I bought to try out, in the V1 spot of most amps I tried they were insanely microphonic. They might be good elsewhere, but I have never bothered trying them again since I still remember the squeal like it was yesterday
A lot of talk about 12ax7 subs, what's wrong with pentodes? OK, I know, small signal pentodes tend to be microphonic. Still, I'd like to see travesty designs like a pentode driving a 12ax7. Yes, 12ax7 as power tube. Crazy? It's been done:
Little Lanilei 1/4 watt Tube Recording Amplifier - Mahaffay Amplifiers Tube Amps, Tube Amplifiers, Amplifier Accessories
LOL.
I'm thinking about the voting system. There should be various 10/1 ratings for each amp: originality, quality of sound, construction skills, etc.
Little Lanilei 1/4 watt Tube Recording Amplifier - Mahaffay Amplifiers Tube Amps, Tube Amplifiers, Amplifier Accessories
LOL.
I'm thinking about the voting system. There should be various 10/1 ratings for each amp: originality, quality of sound, construction skills, etc.
Not how I would do it but then again there are people that like the sound of 12AX7's running on 12V.
Newbie lurker hopes
I found this site and this specific thread a couple of days ago because I was searching the net for plans for a simple, cheap DIY tube guitar amp. It seems like everything on the market is either way too loud or made in China. I have no use for either. Since I've done a few simple mods on an American made Fender amp I thought there was a chance I could actually build one, given good instructions, readily available parts and a reasonable budget. I've got nothing to contribute to your technical discussion, but I do want to weigh in with a plea that the final product include instructions/plans that some of us "nontechnicians" might be able to follow.
I found this site and this specific thread a couple of days ago because I was searching the net for plans for a simple, cheap DIY tube guitar amp. It seems like everything on the market is either way too loud or made in China. I have no use for either. Since I've done a few simple mods on an American made Fender amp I thought there was a chance I could actually build one, given good instructions, readily available parts and a reasonable budget. I've got nothing to contribute to your technical discussion, but I do want to weigh in with a plea that the final product include instructions/plans that some of us "nontechnicians" might be able to follow.