I am utterly shocked that my build seems to work! Plus a few questions

[schoolie]

Thanks for answering my questions along the way.  I powered up my 5f6a and it seems to be working!  It sounds as good as I had hoped, and it's a great feeling.  The only hiccup was reversed OT primaries, so far;)

  I have JJ 6L6GC tubes installed and have them biased on the cold side, I think, 33mA @435V.  I'm not familiar with 6L6 tubes and there is an element in the center that is glowing red, but the gray plates around the perimeter have no red patches.  Can you look at the attached photos and tell me if these tubes look healthy?






Here are a few more gut shots for your amusement:

[LooseChange]

Nice job on the amp!
Those tubes look fine... You can bias them a lot hotter before they'll go red plate.
How did you mount those filter caps?

[jeff]

I'm glad you're shocked because it works and not shocked because it was wired wrong. Good job.

"The only hiccup was reversed OT primaries, so far;)"
Don't feel bad about that, it happens. You got a 50/50 shot.

How's it sound?
You make the cab?
Let's see the front.

[schoolie]

Nice job on the amp!
Those tubes look fine... You can bias them a lot hotter before they'll go red plate.
How did you mount those filter caps?

Thanks, LooseChange!  I made an eyelet board for the filter caps, and there are 220K balancing resistors across each.  There's  a second sheet of G10 board to insulate from the chassis and I have nylon washers between the two sheets as spacers.  #6 screw in the center hold it all to the chassis.  Also used some GE silicone II to keep the caps stable.

[schoolie]

I'm glad you're shocked because it works and not shocked because it was wired wrong. Good job.

"The only hiccup was reversed OT primaries, so far;)"
Don't feel bad about that, it happens. You got a 50/50 shot.

How's it sound?
You make the cab?
Let's see the front.

 Thanks Jeff;)  I'm still scared of electricity so I was pretty careful.  It sounds really good to my ears, and nice touch sensitivity, and very little noise.  It's a tad bass heavy, even with the bass turned down.  I could only turn it up to '3' today, so I'll have to check the high volume later in the week.   I bought the cab from weber, and the finish job is terrible because I was so focused on the electronics:)    I'll post some pics of the front tonight.

 --Rob

[schoolie]

You make the cab?
Let's see the front.

Here are a couple shots of the front.  It's a pretty amateurish finish, shellac and mixol pigment and not much grain filling.

[Davidg]

Congrats Schoolie! Looks like u have done a terrific job-Thats a fine looking amp and Im sure she sounds great too.

[jeff]

" It's a tad bass heavy, even with the bass turned down."

Is it a 5F6-A circuit? You could try replacing the 250 cap(paralleled with the 820 resistor to pin 3 and 8 of first tube) with something smaller (between .1-2.2)
Or try going lower on the .02 cap(from treble wiper) and/or the .1 caps(feeding power tubes).

[Ed_Chambley]

Great Job.  Tubes can run hotter if you want.  Find your high side and your low side for bias.  Play and adjust till it sounds like you want.  It is a Bassman however so it will be a tad bass heavy.  My plates voltage is about the same as yours and I am running 5881 Tungsols.  I found around 40mv to be good for me, but then again some like them a little cooler.

The suggestions Jeff made are good ones.   I made 2 different inputs with different values from pin 3 and another to pin 8.   One is stock bassman and the other is 2.2/820.  Jumper the channels and get about whatever you want.

You've got a great amp, now comes the fun of making it sound just like you want it to.

[mresistor]

what a great looking amp!  Congrats! 

[Platefire]

I laughed when I read your heading because I felt the same way on my first combo build in 2001. If your like me, it ain't over yet------I've been tweaking mind all along the way. I had never had any previous electronic experiance---so as I learned I applied it to the amp in correcting mistakes I made.
Your work looks great, so you may be on better ground than I was.  Platefire 

[Willabe]

Very nice job schoolie!   


              Brad       

[schoolie]

Congrats Schoolie! Looks like u have done a terrific job-Thats a fine looking amp and Im sure she sounds great too.

 Thanks, David!  I would have been clueless without a *lot* of online help.    I'm really happy with it so far.

Is it a 5F6-A circuit? You could try replacing the 250 cap(paralleled with the 820 resistor to pin 3 and 8 of first tube) with something smaller (between .1-2.2)
Or try going lower on the .02 cap(from treble wiper) and/or the .1 caps(feeding power tubes).

Thanks for the tips Jeff!  I'm going to play it as is for a while, and I'll take your advice if I can't dial in my sound.

Great Job.  Tubes can run hotter if you want.
...
You've got a great amp, now comes the fun of making it sound just like you want it to.

Thank you Ed!  Now that I know it's not going to explode, I'll bias it around 40-42mA. I guess it's iterative because the plate voltage changes with each adjustment.   It will be fun tweaking it. I was hoping to add more fusing and a fan, but it's pretty tight in there.

what a great looking amp!  Congrats!  

Thanks, mresistor!

I laughed when I read your heading because I felt the same way on my first combo build in 2001.
....
Platefire  

Thanks, Platefire!  I was so nervous!  I had a bulb limiter, variac, fire extinguisher, and a phone ready to dial 911  I'm already thinking about a 6G2 princeton build...but don't tell my wife

Very nice job schoolie!    


              Brad        

Thanks, Brad!

P.S. I forgot to add my sincere thanks to Doug Hoffman for sharing his knowledge with the el34world site  and selling quality stuff at good prices...and thanks to everybody on the board who provided excellent advice.

[Willabe]

I was so nervous!  I had a bulb limiter, variac, fire extinguisher, and a phone ready to dial 911

Nothing wrong with that. I think it was smart.     

On my first build I turned the amp on with a wooden stick.      


                               Brad     

[HotBluePlates]

" It's a tad bass heavy, even with the bass turned down."

Is it a 5F6-A circuit? You could try replacing the 250 cap(paralleled with the 820 resistor to pin 3 and 8 of first tube) with something smaller (between .1-2.2)
Or try going lower on the .02 cap(from treble wiper) and/or the .1 caps(feeding power tubes).

I concur. If you want to tame the bass, swap that 250uF cap on the first stage with a cap between 1-5uF. You'll keep all the bass you need that way; you can always go slightly smaller if you want to brighten that stage even more, but I'd suggest trying those values first.

The same thing happens in Marshall amps on the Normal channel. The huge bypass cap is (I believe) a way Fender was trying to help get rid of all hum in the lowest level stage. If you planned on playing bass through the Bassman, 60Hz hum is right in the range of your instrument. Fender spec'd a 12AY7 with is supposed to be purpose-made for hi-fi, with low hum and microphonics. However, in any batch of preamp tubes, you might have some which have slight leakage from heater to cathode, which injects hum right into your signal. A very large bypass cap helps shunt hum due to such leakage to ground.

[schoolie]

I concur. If you want to tame the bass, swap that 250uF cap on the first stage with a cap between 1-5uF. You'll keep all the bass you need that way; you can always go slightly smaller if you want to brighten that stage even more, but I'd suggest trying those values first.

Thanks, HBP!  Interesting, and easy enough to try.  Would an 8uF cap be a dramatic change?  I have a bunch of those left over:)

[jeff]

I believe anything lower than 25 will start to do something but the lower you go the more it will thin out the bass. If you have a bunch, you could try two 8uF's in series for 4uF, three for 2.66uF etc. to try out what sounds better, then get that part.

Although I'm not sure that four 8uF is the exact same as using a 2uF as far as responce goes but you could try it to see how changing that cap thins out the sound.

Be sure to check the voltage on the caps(the big ones, not this one) before you poke around. Caps can store high voltage even after the amp is off. I always do this whenever I mod just in case. If there is voltage wait and check again later, it may drain through the 220K resistors but if not get a 10W resistor and short the + and -(careful not to touch anything while doing this) to drain them. Never trust your amp won't bite you, usually you won't find high voltage but if something fails it could, so always check before working on an amp.

[schoolie]

Thanks, Jeff.  I have a 2.2uF polyprop film resistor (Yay, one less electolytic).  I was playing with my Jaguar, last night, and the bass response actually sounded pretty good.  Might not be a bad idea, having a switchable voicing for single coils and humbuckers.

..and thanks for the warning on cap voltages!  I'm always really careful to look (and measure)  before I reach

[plexi50]

Thats beautiful. 5F6A is as good as it gets. I love em. The cab looks great as well

[schoolie]

Thats beautiful. 5F6A is as good as it gets. I love em. The cab looks great as well

Thank you, Plexi50!   I agree, it's a sweet amp design!


I'm starting to notice hum when I turn  the volume past 12 o'clock.  I also notice hiss when I turn up the presence. I guess the chopstick is in my future