6V6 EH-150

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I'm working on this project using only parts I have on hand. My biggest concern is running out of headroom but we'll see what happens. I'm doing the modern interpretation of the 4th series of these amps, I think. Schematic:https://tubeamparchive.com/download/file.php?id=24587

Questions:
I see the diodes in the 6SQ7s are tied to cathode. Why is that?

I imagine screen resistors would be wise? 1K5W?

I'm using AO43 iron, (330-0-330?) , how bout a 400r cathode resistor ?

[M Fowler]

Tino says in his book that pins 4 & 5 on the 6SQ7 tube are detector plates and should be shorted to the cathode to minimize unwanted interference.

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Tino says in his book that pins 4 & 5 on the 6SQ7 tube are detector plates and should be shorted to the cathode to minimize unwanted interference.

Aha. Thanks.

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I want to follow up here, as I'm completely blown away by this amp. Sure it does the CC thing but the breakup is so unique when you push it, even with just the single preamp gain stage. The mic, or overdrive channel has ridiculous amounts of gain, as I don't think it was ever designed for an instrument.
I built a 6V6 version with good ol AO43 organ iron 330-0-330. Wound up with 320 plates 300r cathode and 22V. Even cool like this you can feel things cookin. No grid or screen resistors as per any design.
The bummer is the 8 6SQ7s that I've gone through to get 3 that aren't that noisy and/or microphonic. I still need a good source for the chinese ones.
For the mic channel voltage divider is 1M/82K. 100K was way too much, and 56K killed it. Seems very sensitive here. 50K instead of 100K in the power supply brought the 6Sq7s to at least 100V.
I would recommend this fun to anyone that wants an amp that doesn't sound like anything you've ever built.
The layout was difficult but challenging to try and figure out on a board. This somehow worked out to be quiet :

[img2448]http://www.whiteghostshivers.com/images ... 150gut.jpg[/img]

Here's my voltage chart : [img:960:540]http://www.whiteghostshivers.com/images ... ltages.png[/img]

[JazzGuitarGimp]

I'm sorry, but what does it mean to do the "CC" thing?

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I'm sorry, but what does it mean to do the "CC" thing?

I consider it a very warm and very slightly overdriven tone that only Charlie Christian could make sound clean.

[JazzGuitarGimp]

I wasn't going back far enough! thanks for the heads up. CC is good in my book! (See, I used it in context, just to show I was paying attention!)

[David Root]

I did that one a few years ago out of Tino Zottola's book. 6L6GA and a 5V4G rectifier. Sounds very good. Hums a bit by modern standards but 6SQ7 will often do that if you don't use a DC heater supply.

There are two types of 6SQ7GT, that I call "real" and "fake". See pics. "Fake" is on the right. The "real" ones have "real" 6SQ7GT internals, the "fake" ones have 6J6A internals mounted in an octal case. The real ones are not that easy to find compared with the fakes. I guess the mfrs got stuck with the 7-pin 6J6 internals after WW2 ended so they put them in octal glass for use in AM radios and cheap amps.

I also added a pic of the best 6V6 for your amp, RCA military 6V6GT/G, or VT-107A.

Based on your voltage chart I would definitely put at least 1K screen resistors on your 6V6s, get those screen voltages at least down equal to the plate voltage.

On that divider, I replaced the 100K with a 51K and a 50K pot and put the pot on the faceplate. Works well.

[M Fowler]

Good job on your project.

Here is my tube compliment and I ordered different ones later on but NOS stock is hit and miss for noise.

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Yea JGG, Charlie is the man! If you like his stuff check out Jimmie Rivers "Brisbane Bop". Jimmie was a huge admirer, and perhaps the most underrated or rather unknown guitar picker of all time. He does Rose Room and it's the only solo on the record that he plays note for note like Charlie.Vance Terry may be my favorite steel player of all time too.

David thanks for the headsup on the tubes. I've got all metal ones so who knows what I have. I relied on your build a lot so thanks for that too!

Mark do remember where you got your tubes? I seem to recall that you found some new production Chinese tubes?

[M Fowler]

Mark do remember where you got your tubes? I seem to recall that you found some new production Chinese tubes?

Sorry I do not remember I think it was an ebay source.

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I see the designation is 6G2P. Anyone have any experience with Dawn Audio tubes? The Shugs are a little pricey
http://www.ebay.com/itm/Dawn-Sound-Tube ... vi-content

http://www.ebay.com/itm/2x-New-Shuguang ... 4ac59ebc9c

[David Root]

Mark, my build looks a lot like yours, see pics!

I have recently decided to change mine out to get the original 270V B+ on the 6L6s. Have 375V on the plates now, using C-L-C-R-C power supply and 5V4G rectifier. I found by using PSUD2 that I can use the existing PT (Allen Amps PT25), (325-0-325) and choke (Hammond 158Q) and by changing the 5V4G out to an old used Mullard 5AR4 I have, and rewiring the caps on the 20+20+20+20uF cap can I can go to choke feed L-C-R-C and get 280V B+(!) How lucky can you get?!

It will drop the power output to about 20W or so but that's OK. I will also try adding a 22uF Solen film bypass cap instead of an e-cap to add across the 200r cathode resistor to see how A2 sounds vs A1 operation, and if the audiophile cap does anything nice compared with a standard 20uF e-cap.

[David Root]

Just in case anyone else wants to try this, I did the choke feed/5AR4 mod I referred to in the above post. I just put the first 20uF cap in parallel with the second 20uF cap and disconnected the rectifier output and the choke input from the first 20uF cap and wired them to each other. So easy!

Worked nicely but there is still a little hum. I don't think it's the choke protesting though.
There is something not right in the clean input circuit, have to work on it, the input pot is scratchy but I don't measure any DC on it. It's an old A-B RV4 pot. I didn't check for DC on the grid of the clean input tube. These are old tubes.

Voltages: (normalized to 120VAC)

B+1 plates/screens 284V. Vp=282V, Vs=283V. Cathode 20.0V Need a little bigger screen resistor I think. KenRad 6L6GA, 50mA each.

B+2 PI 244V (6N7). Plates 120/121V. Cathode 2.50V, 2.5mA

B+3 6SQ7 189V. Overdrive plates V2 147V, V3 102V. Cathodes 0.41V, 0.43V, Clean plate V1, plate 102V, cathode 0.46V.

B+2 and B+3 are higher than on the EH185 schematic, which is the only one I found that has several voltages on it. But that uses 6J7s not 6SQ7s.

Sounds so good thru two 2x12s with Celestion Blackbacks that I didn't try A2 operation by adding a cap across the 200R cathode bias resistor. Plenty loud without it! That could change when I put it back in its combo cabinet with only one speaker, a '61 P12N. We'll see.

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I was just considering a speaker for mine. Please do let us know how it sounds through the P12, as that's what I'm aiming for... but it does sound great with efficient celestions.
This is just one of those amps that is just fun to play and it makes putting the guitar down difficult.
I ordered some 6G2Ps, too, so those should be here in 4months. I also randomly found a 6SQ7>12AX7 socket converter thing for cheap...what the heck.
I just went through a whole DC on the guitar pot thing recently on another amp, which sounds different than your problem, but it turned out to be...of course..a crummy "NOS" 12ax7 that was leaking plate to grid, I believe.

Oh, What were your droppers in PS, again?