coresta said:Hello , yes , i'll scan the schematic in a few days : i still have a low hum (on 515 woofers ..) but would like to cancel it . I operate them with 300/0/300 PT / 5R4WG /2x2uF polypro /10Hys /32 uF . There is 325volts on the OT (3,3k primary ) and G2 is tied to A with 47ohms WW. G2 to the center of a 30ohms pot to 750ohms WW (+47uF 63volts) to GND. Heater is fed through 2 WW 0,39ohms resistors to the 6,3Vac . Grid leak res : 255k MF . The red block is a coupling silver mica capacitor 22nF /500v . The input tube : A 10k decoulping resistors goes to 32uF to feed a 6C6 with 80k MF in anode , g2 : 900K MF /0,22uF and Rk : 1,21k MF //47uF tantalum . The Ammeter in cathode goes to 45mA . Silver teflon wiring and iron plateSound is astonishing for such a low power of 6 watts. Smoth and grainy . Bass is ... good , not so hard as with my 50W OTLs but they would perform for driving a 299/805 combo ! I've build a pair and will modify them for a 423C gas regulator in the 6C6 screen grid . As Tubelabe says , the 307As are worth the effort for the 15 Euros each i found them
Coresta,
Here is the Radiotron 6C6 amp and the link to Joseph Esmilla's site where it is discussed.
An externally hosted image should be here but it was not working when we last tested it.
http://members.myactv.net/~je205d/6c62a3.htm
Look forward to your schematic,
-- josé k.
I wouldn't call the 307a "today's components" since they are no longer built, when 300b's, 2a3's, etc, are.
I wouldn't call them easy to find anymore either. I've been trying to find a pair for months now. Everywhere I check is out of stock, or are charging 60-100 per tube. (while the out of stock places were charging about $15) I did manage to get a pair from 2 different vendors, but each tube was different! now I have 4 tubes w/ different construction! I just want a pair where each tube looks the same, and I want to pay less than 300b prices!!!
I wouldn't call them easy to find anymore either. I've been trying to find a pair for months now. Everywhere I check is out of stock, or are charging 60-100 per tube. (while the out of stock places were charging about $15) I did manage to get a pair from 2 different vendors, but each tube was different! now I have 4 tubes w/ different construction! I just want a pair where each tube looks the same, and I want to pay less than 300b prices!!!
The mere mention of certain number depletes stocks and skyrockets prices.
i don't have interests in pmillet business , i (almost) never buy any tube charged more than 20 bucks/unit as i still have 12 307a sparelife stock 
Merry new year!
Just resurrecting an old thread...
I posted some info on the 307A tube, and a push-pull amp design I've been working on for a while:
http://www.pmillett.com/307a_pushpull_amp.htm
Sorry if my site is loading very slowly - a guy at EDN magazine posted a link to my books page and the site has been getting hammered. I might hit 1TB of data transfer this month
Pete
Just resurrecting an old thread...
I posted some info on the 307A tube, and a push-pull amp design I've been working on for a while:
http://www.pmillett.com/307a_pushpull_amp.htm
Sorry if my site is loading very slowly - a guy at EDN magazine posted a link to my books page and the site has been getting hammered. I might hit 1TB of data transfer this month
Pete
pmillett said:Merry new year! . . . . . Sorry if my site is loading very slowly - a guy at EDN magazine posted a link to my books page and the site has been getting hammered. I might hit 1TB of data transfer this month
Ahhh , so that's what happened. I wondered what was up when last night i tried to download the STC file. When it still wasn't finished after half an hour I took a look at the download bar. It read "7 days , x hours etc. remaining" ! Hah ! I got it today in a couple of minutes.
Happy New Year to you too Pete.
Big thanks for all you do, like keeping that site up and running. It's a valuable resource for all of us and it's really appreciated !
I still have my Tubelab SE running with the VT225's in it. I just wired the VT225's in place of the Chinese 300B's and the amp sounds better than it ever has (never tried high dollar 300B's though). I wired G3 to ground just because it seemed like the right thing to do. I will try connecting it to the plate the next time I have the amp down on the workbench.
A few years ago I plotted curves (manually) on an EL34 connected both ways. The G2 = G3 = Plate connection definitely showed some signs of "tetrode kink" that was not present with G3 tied to the cathode.
I plan to try a pair of the VT225's in push pull in the near future. My old favorite P-P amp the 300Beast has blown another power supply cap, so it is currently dead. It is the only amp that I made in the "pre Tubelab" days that I still have. I think that it is overdue for a rebuild.
While I was up north I designed a "universal P-P driver board". It is similar to the 300Beast driver but far more flexible. I plan to "test" a bunch of the sweep tubes that I collected during the tube sales that several vendors ran last summer. I will also experiment on some VT225's and a few other WWII surplus tubes that I have.
astouffer said:
I have an HP 8903A audio analyzer. They are reasonably priced in the used market (unlike an Audio Precision box). I think I paid $900 for one freshly calibrated from an instrument rental company.
By itself the 8903 doesn't have any good way to make graphs, but it is fully programmable and controllable through GPIB.
A while ago I bought a copy of HP VEE, which allows you to make test programs using a visual interface. The plots you see were generated by test software I've written for VEE.
A runtime-only version of VEE is available for free... so I was thinking of posting my programs so that somebody with an HP 8903 could use these. So I was about to post a topic to see if there are any 8903 owners who want to be the beta site...
Pete
Yep, I've got one too. I got it for $75 in non working condition. I fixed it. It has died, and I have fixed it again something like 3 times in the 10 years that I have had it. No GPIB card yet but they shouldn't be too hard to find. The trick is finding one with suitable drivers for VEE. I will be willing to experiment with your programs.
It will control an analog XY plotter. Unfortunately mine died several years ago and those have become hard to find.
If you a copy of LabView someone has written a driver for the 8903A. Its available from www.ni.com
Does anyone know where to get these tubes?
I've been searching for years now! When I first started looking EVERYONE had them, and I got a couple. But, I wanted some spares a couple of months later and no one had any. I'm on the waiting list (or was) at several different tube brokers.
So, anyway, I haven't been using these tubes in my amp anymore because they do sound very good, and i'm sort of saving them for special occasions. I'd love to have a spare set so I can listen to them w/out fear of it being my last time.
I've been searching for years now! When I first started looking EVERYONE had them, and I got a couple. But, I wanted some spares a couple of months later and no one had any. I'm on the waiting list (or was) at several different tube brokers.
So, anyway, I haven't been using these tubes in my amp anymore because they do sound very good, and i'm sort of saving them for special occasions. I'd love to have a spare set so I can listen to them w/out fear of it being my last time.
I'm not sure of this is a violation of the forum rules (if so, moderators plese delete my post!)... but since people have been having a hard time finding 307A's I thought I would mention that I just listed a few 307A's (singles and matched pairs) on ebay at what I hope is a reasonable price...
Terrible, having more tubes than money
Pete
Terrible, having more tubes than money
Pete
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