Blonde Bassman 6g6B clone - Arc of My Amp

[HommeMarrBuckley]

Hello everyone,
I will keep this short.  Currently, Im waiting on some parts and head cab is glued/clamped up and had some time, so I thought, I really should finish out my Blonde Bassman 6g6B.  I would have posted sooner but you know life can get in the way, just moved to FL this year among other things.  But I owe it, and want members to know that I closed this out.  Bottom line, there's no hum, and its pretty f-n loud.  It was all built stock except that I added bias points and removed the treble bleed cap from the bass channel which is noticeably louder.  Honestly, I don't get the mystique of just using the normal channel.  Im beyond ecstatic for the tone and clean this thing achieves.  I am keeping it destructured--(faceplates, tolex)--First, out of graphic design frustration, laziness, and then a grown fondness.  The 7 coats of tung oil really paid off--as they should!!
A supreme thanks to admins and members that helped me out along the way.  Great Forum! I would say that I am perfect example of someone that didn't know anything (that still doesn't know/understand much--will be here with new builds) that was able to produce something that exceeded my expectations.
This is third and final post  (was done a long time ago but some things take me a while sometimes)
Here's memory lane:
1st: http://el34world.com/Forum/index.php?topic=16153.0
2nd: http://el34world.com/Forum/index.php?topic=18022.0
Thanks everyone

[sluckey]

Looks nice.

[eleventeen]

I like the look of it as it is, having no faceplate doesn't bother me. It's very nice!


The only thing I would suggest is to move your breakfast up to the table where it is much easier to eat!

[shooter]

move your breakfast up to the table where it is much easier to eat

I was thinking he used the table to make the cab

[HommeMarrBuckley]

The only thing I would suggest is to move your breakfast up to the table where it is much easier to eat!

 

I was thinking he used the table to make the cab

Put than in for IDing purposes, but that plate was hot, so on the floor it went, last thing I wanted was the bottom of it marking up that easily dingable pine.

[HommeMarrBuckley]

Hello everyone,


I was recently playing with this (Bassman 6g6B clone) and realized that I never really properly biased it, however, without doing this all the time and experience with other amps, I just wasn't sure.  I slid out the chassis and am now looking to put it back together but not until I feel good about the readings.


I have winged C 6L6 GC output tubes in it so that's the other concern--considering their value has gone up considerably and dont want to damage them.


Started pin 3 was 453 and 35.2 mV at about  15.9 which seems well under the 23 watt max
Adjusted
pin 3  438 (about 10 Volts over on schematic) and 37.8 mV at about 16.5--still under


Just wondering if I should continue because I feel that I am not getting near proper use out of them--I get the notion that I am running them fairly cold. (I realize that if I run them hotter the tube life is less)
but just thinking I will be fine if I open it up a bit more because they dont appear to be running too warm.


Just wondering thoughts.

[sluckey]

I like to set fixed bias amps for 70% of max plate static dissipation. I'm not sure where you got the 23 watt max number but your 15.9 number is 69% of 23 and your 16.5 number is 71.7% of 23. I'd be happy with either of those numbers.

[PRR]

"6L6GC" *should* be good for 30 Watts. That's what the "GC" means.

GC also allows 450V on screens; most older types did not.

23W is the older 5881 type (a beefed 6L6G). Original recipe 6L6 was 21W at first, quickly rolled back to 19W rating.

I am wary of a full 30W dissipation on many 6L6GC, I think that is right on the edge of long-term life.

I would NOT be afraid to run good 6L6GC at 20W-25W forever.

You could come up a tad from 16W Pdiss. However there will not be a big change. Try it. If you don't go "Wow", let it idle cool.

[HommeMarrBuckley]

I got the 23 watts from the Lord Valve piece (excellent piece that you forwarded from another post-thanks Steve)
http://www.duncanamps.com/technical/lvbias.html
(Table A at end of article)


Yeah, I was thinking of putting of putting it back in the cab but was checking out the Weber Bias Calculator and was considering trying the low 40mV range.


The spec sheet for the newer tubes states for typical operation of two tube Class AB operation for plate voltage at 450V and bias of 37V which is close to where Im at.
http://tubeaudio.com.au/content/tube_data/wc/6L6GC.pdf
It seems to be fairly safe, I just don't know because these tubes don't seem to be glowing as much but what do I know.  It's hella loud for sure which somewhat complicates things.


I was thinking of just getting the plate voltage to where the schematic has it.
Stuck between thinking it's safe and don't mess with it because Ill end up frying the tubes but then the thought of someone coming along and saying the whole time I could have opened it up a bit more and it would have been fine.


-just read PRRs post-
this is pretty much what Im after--opinions/thoughts--when you're alone without experience and no one really to turn to I thought it best to pause and post

[PRR]

> I got the 23 watts from the Lord Valve piece

For 6L6GC:

The factory datasheet says 30W.

Lord Valve's opinion was that a fix-bias guitar amp should not run hotter 6L6GC than 23W, and probably less.

23/30 is 77%, in sight of the wide-target "70% rule".

> these tubes don't seem to be glowing as much

As Lord Valve said-- most of our tubes should NOT show plate glow at idle.

The ends of the heater must, of course, run red-hot. The brightness will vary from maker to maker and with production changes at the same maker. The ends are not the important part of the heater.

> It's hella loud

The idle bias current has almost NOTHING to do with how loud it will go. Think of a (pre-computer) car. You could set the idle RPM low, 400RPM, or high, 1200RPM. This would affect battery charge and traffic-jam overheating, but did NOT affect the power you got when you MASHed it and revved to 4,000RPM.

A too-cold tube amp can be "rough" at very low volume. We almost never hear of complaints like this. The usual 40%-80% biases are smooth enough for all rock/blues/jazz.