7-pin tubes

marshman · Post by **marshman** » Tue 08/26/08 4:40 pm

So, I've gotten my hands on some 6AQ5s, and am considering a sort of single channel TMB type amp to use them. I have some 6X4s, which are rectifiers of a 7 pin persuasion, but I've no idea if they're useful. I would like, if at all possible, to build this little monster using all 7 pins, but I've no idea if there are any preamp tubes that'll work. Anyone checked this stuff out?

Thanks!

57chevy · Post by **57chevy** » Tue 08/26/08 5:07 pm

6AV6 or 6AT6 is the same as 1/2 of a 12AX7. Fender Harvard 5F10 uses one.

http://www.schematicheaven.com/fenderam ... _schem.pdf

marshman · Post by **marshman** » Tue 08/26/08 8:16 pm

Well, that's a start--I've got a pair of those. Any other suggestions?

Would a standard set of 18watt trannies be a bad idea for this project? I'm pretty sure the heater current requirements would be roughly the same, but that's all I can decipher from the data sheets.

Depending on the chassis I find, I may go all-out with the features...triode/pentode...switchable rectos...maybe a '36 watter'...The mind boggles.

Thanks, 57chevy.

Post by **CurtissRobin** » Tue 08/26/08 10:20 pm

The 6AQ5 has been mentioned often on these boards. A search for 6AQ5 got me 64 hits, many of them guaranteed useful. The 6X4 is a rectifier tube that's been used in ECC83 - EL84 amps. A recent ebay auction was for a couple Bell and Howell amps built for U.S. Army movie projectors with 2 or 3-12AX7, 3-6BQ5 and 1-6X4 tubes IIRC.

As for iron, check the P-P plate impedence and match that. According to the RCA manual the 6AQ5 is essentially a 6V6 with a different envelope and lower operating limits. The 18 watt OT should do fine.

In fact, your timing is great: go tho this thread for clips http://www.18watt.com/modules.php?name= ... ic&t=20061

KennyO

marshman · Post by **marshman** » Wed 08/27/08 7:34 am

Well, I use this http://www.nj7p.org/Tube4.php?tube=6aq5 for info--are you referring to plate impedance, while the data sheet calls it Plate resistance? The number given on the sheet is 60K ohms, which doesn't sound right to me. The only other figure given in ohms is the 'load resistance', which seems a bit more realistic at 10k...(http://www.18watt.com/files/6aq5.pdf this data sheet calls it ' effective load resistance, plate to plate)

I did look through a few of those, but most were mentions involving 'lowering output' questions. The Selmer schematic and Alexos' 6x 6AQ5 were interesting, but they don't seem to have PT/OT data that I can understand, and most of the jargon was beyond me, I need information in smaller doses or my brain locks up.

I'll have to wait until later, when I get to my PC to check those mp3s. My laptop is total crap for listening to those.

Thanks

morcey2 · Post by **morcey2** » Wed 08/27/08 8:46 am

On the nj7p.org pages, you want to look at load resistance.

I built a mongrel of an amp using a pair of 6AQ5's that I think sounds great:

http://mcorey.dsl.xmission.com/blues_thingy/index.html

The B+ is pretty low at 205V so I'm using a 5K OT. For 18-watt type voltages anywhere from 6.6k to 10k should work well. The sound of the 6AQ5's isn't as round as a straight-up 6V6, but isn't as bright as the EL84 so it's a pretty good compromise if 6V6s are too dark for you.

As for 7-pin triodes, look at the 6J6 or 5844. They're dual triodes with shared cathodes so they would work well as a PI or as the first stage in a Lite or normal channel of a trem. Not sure how they would sound, but they're out there.

Another tube to look at is the ubiquitous 6AU6 pentode, if you're looking for that type of sound.

Matt

dotfret · Post by **dotfret** » Sun 08/31/08 5:37 pm

You really want to do this?

The best single triode substitute for half a 12AX7 is a 6AQ4 /EC91. These are effectively half a 12AX7WC, run at a high heater current (300mA each) to keep the noise down - the gain is accordingly about 5% down on the specification, which is about 12% less than a fresh NOS Mullard 12AX7A. If you can provide the extra heater current, you can buy genuine RCA or Mullard CV417 / EC91 / 6AQ4 very cheaply. And they do look cute, with those little panels up the side that make them glow blue ...

marshman · Post by **marshman** » Sun 08/31/08 11:12 pm

I might go down this route, I might not. I think it would be cool to have an amp with all 7-pin tubes. Heck, at least the nI wouldn't be fightin with you guys for all the good 84s on ebay. Mostly, it's something to think about so I don't go crazy. A man's gotta have hobbies, right?

I'll have to pour over some existing schematics using these tubes, as I've no idea how to create a circuit from scratch. Best I can do is 'Well, I think I'd like something TMB-ish", so I'll have to figger out what sort of trannies I'll need.

Thanks for the input, folks. 6AQ4 preamp, 6AQ5 power amp--I like the logic of it.

veets · Post by **veets** » Mon 09/01/08 2:15 am

I tried 6J6's as a preamp--didn't work too well for me--I switched to 6AV6's, diodes tied to cathode--works great. One 6AU6 and one 6AV6 would likely be VERY interesting. Another excellent sounding preamp tube, IMHO is the 6BZ7, but it's a 9 pin.

Phil_S · Post by **Phil_S** » Mon 09/01/08 2:42 pm

Treat the 6AQ5's exactly like 6V6's. They are the same tube. The only caution is that you should stay much closer to design center specs on plate voltage, as I don't think the small bottle will take as much heat. I have run 6AQ5's plate voltage as high as 335v, but suggest you are pushing it too hard past about 300-310.

Donations

Links

Welcome

7-pin tubes

7-pin tubes