New Year's 6AV5GA SET project

[Sal Brisindi]

Ed,
I just found a stash of 6AV5 tubes, might be a fun project to build with all the junk box parts I have on hand... Edcor audio's, no name surplus power transformer and choke.....

Sal

[EWBrown]

These 6AV5GAs are pretty neat tubes! I also have lots of 6GE5s, 12GT5s, and other similar duodec and novar horixontal sweep tubes, to try out sometime, after my eyes get better. A while back I did some static testing of 6GE5s and ran them, cathode-biased with 1K and also 820 ohms, up to about 25 Watts of PD with no ill effects.

Right now, I'm seeing through a "smoky, fuzzy fog" from the "floaters" - the right eye was the first one, now the left one is starting to be effected.

What I do is go ahead and touch- type, then when I read the newly posted text , I can set up for a larger font, and then I can generally find any egregious typos and blunders It;s a bit slow but it seems to work for now...

Fortunately there are no torn or detached retina problems, and it will get better over the next few weeks (or months, or years...), and I am under an optometrist's care for it.

It is somewhat hard to read, and watching DVDs isn't too good either , so I'm listening to a lot of radio, and tube amplified music to help pass my time. if anything, maybe my touch typing will improve

There's a blind guy over at the Bottlehead forum, if he can build amp kits, I am sure that I can learn to deal with somewhat fuzzy eyes for a few weeks...


/ed B

[Sal Brisindi]

Hi Ed,
I wish your eye's a speedy recovery.

Regards,
Sal

[EWBrown]

Thanks! THe right eye seems to be a little bit clearer - or perhaps I'm just getting used to foggy vision, but now the left one is starting to develop more than the usual background number of "floaters", but so far it is not as bad as the right one.

It's just gonna take some time, I just have to be patient, and let nature take its course

/ed B

[EWBrown]

I have my (hopefully) final eye test for this situation scheduled next week (March 22nd) , then I can get a new perscription for glasses, if the eye doc says everything seems OK.

Still a few streamy floaters and small foggy "clouds", but I've learned to deal with them, and I hardly notice them now. At least no surgery or other serious treatment was necessary.

/ed

[DeathRex]

I built Ed's version of sorenj07's 6AV5GA amp. I'm getting pretty nice sound, but I'd like to get a bit more sesitivity. With 1VPP into the 6DT8, I have 42 volts out, and 2.9RMS volts at the speaker. With 2.6VPP (max out of my CD player before clipping) into the 6DT8, I'm getting 100 volts out and 7.1RMS volts at the speaker. With a Pioneer tuner plugged in I never get to clipping and only a max of 2RMS volts at the speaker.

Only difference I made was a yellow LED on the cathode of the 6DT8. It's running right at 3ma. My B+ is 310 and the output transformer is a 3.5K to 8 ohms and I have 295 VDC on top of the 6DT8.

[DeathRex]

Well after looking round I replaced the SRPP 6DT8 with a cascode 6DJ8. The gain is massive, 200. It's a bit less with a 6N23P and even lower with a 6N1P, but I can swap tubes without changing anything for testing.

[msmpe]

I'm just finishing up my 6A*5GA SET. B+ is 305V to the OPT and Rk is parallel 1K+1.8K-2W CC resistors bypassed with 100uF, for about 67mA. Signal amp is unbypassed 12AX7 (shielded) grounded cathode with a gain around 40. The amp worked very nicely on my bread board, even though the OPT are the inexpensive P-T31 from AES, surprisingly good bass, clean highs. PSU is 235V with FWB to CRCRCLC, and the FS is FW rectified - hum is NOT acceptable!

I like that tube!
I'm using Sylvanias. I tested the bulb temp and it is no where close to max spec. I'll post a couple photos when I get it tweeked and broken in.

[EWBrown]

I recently, about 2 weeks ago, completed this amp's "second generation", usig 12AT7 SRPP driver, and 12AV5GAs, and wired the two 6.3 vac filament windings in series, for 12.6VAC. Why? Just because it could be done, and more importantly, because 12AV5GAs are even cheaper than their 6V filament brethren.

I used a PA774 power trannie, and a variant on the ST-35 power supply circuit, but with the addition of two more chokes, after the C354 choke and second electrolytic, making this a "split "CLCLC supply with each "second" choke and "third" cap feeding one 12AV5GA. The idea was for (hopefully) more power supply isolation and separation for the power stages.

RK for each 12AV5GA is 880 ohms, 25W Dale "heatink" resistors, bolted to the chassis, and each bypassed with 47 uF / 160V electrolytic, and 10 uF / 200V film cap in parallel. With about 375V B+ and the James 6112HS3.5K: 8 ohms OPTs, I get approx 66 mA (58 VDC) through each of these resistors.

With these numbers, I'm running the DuMont labelled Sylvania 12AV5GAs at 20.6 watts PD, and they run quite "happily" with this level of plate dissipation. So much fortheoverly cautious 11 wat tratings for these tubes - just be sure that these have the larger plate structures - the DuMont / Sylvanias do, but not all RCAs will have them..

I carried the film cap bypass technique to the two OPT B+sources, and to the 12AT7 SRPP driver stage's electrolytic, with Solen 4.7 uF / 630VDC caps, it may seem trivial, but these added film bypass caps made a dramatic improvement in the sound quality, with much clearer higher octaves response..

Photos to come soon...

/edB

[msmpe]

Well, I finally got it singing, but my PST can't hadle the load, so I ordered an EXPWR050 from Edcor. Been running it off my Heathkit PS2.

Sounds really good. Makes the Bose 201s sound good, much better than the transistor amp they were tied to. I started with some Miles Davis electric stuff and wow really rich, then tried Chick Corea electric and ditto very rich, then cranked it and put some Charlie Musselwite on - in my garage/workshop at 3/4 knob and sat about 15 feet back from the speakers: very clean mids, good bass, nice highs, it sounded like I was at a concert but with much better clarity than the PA stuff.

I can recommend these tubes to any one looking for inexpensive tubes. I'd like to try these in PP like the Bogen (DB225 ?).

[EWBrown]

I've been doing some "static" testing of 6GE5s, with the Heath regulated power supply, and various cathode resistor values (820, 750 and 620 ohms). And varying the B+ from 240VDC all the way up to 400VDC (with the 820 ohms, lower voltages with 750 and 620 ohms).

6GE5s (and their 12V and 17V filament versions) are 12 pin duodecar compactrons, and are available for relatively low cost, $5 and under.

6GE5s look very promising, these are heftier than the 6AV5GAs, with a 17.5W PD rating and 3.5W G2 rating.

I'm getting very nice looking results with B+ of 360 to 380V, and 60-66 mA cathode curent.

Running my tabulated results against SE-CAD, the 6GE5s operate extremely close (within 2%) of SE-CAD's 6B4G and 2A3 SE simulations.

FWIW, 6AV5GAs run very close 300Bs on Se-CAD simulations, within their "extended" 20W PD and max of 400V B+ limitations, on SE-CAD.

/ed B

[EWBrown]

It has recently spawned a 12V version...


http://www.diytube.com/phpBB2/viewtopic.php?t=5497

/ed B

[EWBrown]

More 6AV5GAs, revisited on DIY Audio: (I linked this and two other of my 6AV5GA related adventures at the bottom of their third page on this topic)

http://www.diyaudio.com/forums/tubelab/ ... e-amp.html

I just hope that this doesn't start some kind of space-time-loop-discontinuity divide-by-zero error