6AQ5 Express -- It's amazing!

[Phil_S]

I've corrected the flying leads for presence and the grid input by running them under the board like I should have to begin with. You can't take short cuts! I found a length of teflon jacketed shielded twisted pair for the grids. I also used shielded for the long run from the volume pot to V1. So, I can't be 100% certain what fixed things up, but likely all three things needed doing.

What's amazing is the way the guitar volume control works with this amp. It seems not to add much volume, but functions more like a grit control. Turn it up = more dirt, down = more clean. I only had time for a 10 minute test drive, but this amp clearly has a unique character and plenty of tone. It's very articulate, too.

It still needs a few tweaks, but really, this one is nearly finished and came out very well.

Thanks to those who helped.

Phil

[doctord02]

Phil, did you make this fixed bias or self biased like a Liverpool? If the latter, what size resistor did you use? I havent built with 6AQ5's before...

I have a similar build in the works... with 4x6AQ5's and a half power switch that defeats two tubes, plus a Komet style fast/gradual switch.

[Phil_S]

Except for the iron and the B+ supply ladder, I followed the Francesca schematic. Some of the components aren't the "right stuff" but they are the stated value on the schematic. This is a fixed bias amp. I added test points and the bias pot is a regular pot you can adjust from the deck of the chassis. Setting the bias is a snap.

The PT, rated 275-0-275 is running on the lowest turns ratio available on the pirmary and puts out about 262-0-262. The mod to the supply ladder was to use a 9k1 between B+2 and B+3 instead of 18k2. This left the preamp at very close to the voltages published on the schematic.

The iron is from www.musicalpowersupplies.com. Can't get much cheaper than that, but it seems to be good stuff.

The 6AQ5 is nearly identical to the 6V6. Treat is exactly like you would treat a 6V6. The only caution is that the small bottle won't take the heat of high voltage. Where you might run a pair of 6V6 at 375-400v, that is probably too much for 6AQ5's. This amp is idling with Va =~330vdc and grid at around -22v. This is giving me about 15W give or take. It was great to be able to match tubes right in the amp. I would be disinclined to push a 6AQ5 beyond where mine are. In a SE amp, I would stick closer to the design spec of 250-275v.

Good luck with your build.

[harryk]

Congrats Phil! It is always a big pleasure to get one amp ready and sound like you planned. Did you say that you really get out 15 W of that with those tubes? It is pretty near 6V6 tubes with those voltages. My aim is to have maximum 7-8W out of those EL95 tubes. Regards Harry

[sliberty]

Phil - geat to hear your happy with the results. Now we need pictures and clips

[Phil_S]

Congrats Phil! It is always a big pleasure to get one amp ready and sound like you planned. Did you say that you really get out 15 W of that with those tubes? It is pretty near 6V6 tubes with those voltages. My aim is to have maximum 7-8W out of those EL95 tubes. Regards Harry

Harry (or anyone), please check my math on Pout. In round numbers:
Va=330, Ia=23
Pout = .023 * 330 * 2 tubes = ~16W
Am I doing this wrong? I'm asking if I should or should not multiply by 2 tubes. For some reason I don't understand, I've got a bit of a mental block on the math.

If you bias the EL95 up near spec, which is 24mA at 250v, then you will get 6W per tube. At 70% times two tubes, that's about 8.4W for the pair. So, yes, 7-8W sounds about right. If you build this out like Francesca (forgive me as I may have said this before) with a 250-0-250 PT, I think B+ will be around 315V. If this is the case, I would expect the bias supply, which has a range of about -20v to about -33v might be a little on the cold side.

In truth, though, 8W will still be loud (about 90% as loud as 16W). In my experience, you need to get down in the 2W or under range to get overdriven sound at conversational level. Unfortunately, 2W doesn't push nearly as much air out of the speaker and you lose the "feel" of it.

May I suggest you look at the ECC99 dual triode for a self split output tube? You could really work some wonders with this tube and it will be in the 2W range.

[Phil_S]

Phil - geat to hear your happy with the results. Now we need pictures and clips

Pictures today, clips maybe later. I'm a terrible guitar player and have not been playing lately. I need time to explore this amp, too.

It looks like 3 pix is the allowed limit. I should take some lower res pictures.

[harryk]

Phil! I am not that good in math, but my guess is that with a pair of EL95 you only get out max. 7-8 watts which is ok for me. I made one small amp with 12AU7 in powerstage and do not like too much of it. Maximum plate dissipation is not the same as output power. If an amp is well optimized, it can push out max. half of max. plate dissipation. You have a nice looking amp. What kind of cab you are aiming to do to it? I have a friend of mine who can do anything of wood. I order all my cabs from him and finalize them myself with tolex or laquer etc. Regards Harry Bluetone

[Phil_S]

If I can find some reasonably priced wood, I have a dovetail jig that will do a nice job on a cab. I've got some grill cloth left over from another project.

Otherwise, it will get screwed to a #2 pine plank until I can get to the cabinet.

[doctord02]

Thanks for the info Phil. I'm running at a lower voltage using an Edcor 190-0-190 200ma PT. I dont expect I'll get much clean headroom.

Your build looks good, and I'm jonesing to hear the clips...

Dave

[skyboltone]

Hey Phil:
Do the points of the chicken heads run into each other being so close??

[Phil_S]

Hey Phil:
Do the points of the chicken heads run into each other being so close??

I measured very carefully. There is enough clearance. I'm partial to chicken heads.