HUUUUUMMY new build

[Robert M. Martinelli]

So, here's what I've found...

I strung three 1N4007 diodes together in series after the DC cap(s), and with the tubes in and warmed up, I'm getting about 8.5vDC before the diodes (this being down from 9.56vDC...thus indicating the load of the tubes), and about 6.07vDC on the tube filament pins. SO, this is great! That's just where I want to be.

So, I assume then I'll need to find a resistor that would drop the same amount of voltage as the diodes. If memory serves, the diodes drop .7v each, so I'd need a resistor in the range of 2.1 ohms, yes? Probably about 5w?

Lemme know if I'm doing the math correctly...I'll place the order from Mouser tomorrow. I'm thinking nice silicone coated wirewound power resistors....

Hi,
The drop across the diodes is about 2,4 V ( 0,8 V each, the voltage drop across a diode increases together with current because of its differential resistance ), you obviously need the resistor to drop the same voltage, and the sum of the heaters' current, if memory serves me well,is 2,1 A, so you'll need the resistor to be R = 2,4V/2,1A=1,15 Ohm.

As to the resistor's rated power, 2,4V*2,1A=5,04W, so a 5W resistor will work at its limit, thus heating considerably, so I'd rather put in a "10 Watter" for peace of mind. Since 1,15 Ohm is not a standard value, you could use two 2,2 Ohm 5 W resistors in parallel, ( BTW, this will put you a little closer to 6,3V ).

HTH

Best regards

Bob

[dehughes]

Hey Bob...thanks so much. I think you're right on, save for the current draw. It's just one 12AX7 and one 6SN7 that will be run on the DC system, so that's only .9A. In that case, a 5w resistor should be just fine.

I'll order a couple resistors in the 2 to 3 ohm range, just to be safe.

Thanks!

[tedmich]

would putting the heater CT on the power tube cathode have helped here?

[dehughes]

would putting the heater CT on the power tube cathode have helped here?

Might have. I just didn't want to un-do the wiring, AND I was kinda looking for an excuse to try out DC heaters.

That said, I put in a 12.6v filament transformer, two MUR410G diodes running to two paralleled 10000uf caps, into a 2.5 ohm 5w Dale RS resistor, onto another 680uf cap, and then on to the heaters. 6.1something VDC. No hum.

Good enough for me.

THANKS TO YOU ALL. I hope my tinkering/trials/ignorance/stupidity here can be of benefit to others in the future...

[bnwitt]

If you hook up that same scope to a wall outlet, you will see 339.36 VAC pk-pk.

No I don't think so. 120 VAC RMS would be 169.68 volts peak to peak when measured to the grounded neutral of a home wall outlet. Your number is for a 240 volt service which is the differential between the two out of phase 120 volt legs of a residential service.

[erndawg]

No I don't think so. 120 VAC RMS would be 169.68 volts peak to peak when measured to the grounded neutral of a home wall outlet. Your number is for a 240 volt service which is the differential between the two out of phase 120 volt legs of a residential service.

That's not right.

(120 VAC RMS)(2)(rad 2) = 339.36 VAC pk-pk

Try using your o'scope and experience it first-hand.

[erndawg]

Your number is for a 240 volt service which is the differential between the two out of phase 120 volt legs of a residential service.

Also note that in a 240 VAC service it is not a *differential*, but rather an additive effect.

[bnwitt]

Also note that in a 240 VAC service it is not a *differential*, but rather an additive effect.

I'm sorry but I just have to throw the bullshit flag on that comment. It is indeed a difference or differential between the two waves which produces the 240 volts potential. Each wave is 120 volts RMS from 0 but since they are 180 degrees apart in phase, there is a resultant potential of 240 volts between the two waves. Your additive comment is semantics. Of course the difference between the two opposite polarity waves is additive. What else would they be? It is the difference between the opposite polarity waves that provides the full differential potential. We are talking the number scale here. 6th grade math. And I think the disagreement we keep having here is due to the fact that I keep using the phrase peak to peak voltage when I mean simply peak voltage. In a 3 phase system the legs would be 120 degrees out of phase and have less than two times the RMS voltage based on the square root of three. So individual legs of 277 would have a potential of 480 volts between two legs. 277 times 1.7321 which is the potential difference between the two legs.

[erndawg]

I'm sorry but I just have to throw the bullshit flag on that comment.

Wow, that's a pretty unnecessary personal attack.

In my posts 54, 59, and 66 I tried to explain to you the relationship between RMS and peak-to-peak AC. Your response is to be insulting to me to skirt your technical gaff.

Your additive comment is semantics.

It is absolutely *not* "semantics. If they were differential, the voltage would be something less than 240 VAC depending on the phase relationship. "Difference" explicitly means subtractive, not additive.

[bnwitt]

Wow you are thin skinned Erndawg. My statement was in no way a personal attack on you but a statement as to the validity of your comment. I clearly referred to the comment not you personally. You took my post the wrong way. No personal insult was intended.

But again, I disagree with your definition of difference as being only subtractive. But, by disagreeing with your point, I am in no way personally attacking you. You seem to be hung up on the semantics of the terminology. Let me see if I can explain my point better:

What is the potential "difference" between negative 120 and positive 120? That would be 240 as long as the voltages are 180 degrees out of phase. Now how is the deriving of that potential difference number at all subtractive? It is not, it is additive.
Read this:

Potential difference - Wikipedia, the free encyclopedia

Now I realize my use of the term "potential difference" is somewhat old school, but I'm and old guy. By the way, your characterization of me as someone who personally insulted you to cover up a technical gaff is certainly a personal attack. But I forgive that as you obviously were laboring under a misconception of my intent and were retaliating.

[erndawg]

Look, there is no need to shout or be condescending.

Wow you are thin skinned Erndawg.

You certainly seemed a little thin-skinned over LoudThud's comment.

Place nice, Barry.

[bnwitt]

Erndawg,
you need to learn humility. You're full of yourself. I have now lost all respect for you. Have a nice day. Your are a manipulative self serving soul. Good luck quantifying your intelligence by posting snide comments on forums. That is precisely why you don't respond to the essence of my posts but just continue to personally attack me. You have some pitiful need to make yourself feel superior. Take a hike Ernest. I won't waste my personal time responding to any more of your posts. You're a sad little man with internet access. A star for a very brief moment. Go back to your mundane day job.

[erndawg]

My statement was in no way a personal attack on you but a statement as to the validity of your comment..

Your link to the Wiki article is unnecessary.

In fact, it is you who does not comprehend the fundamentals as evidenced by your statements in posts 51, 53, 57, and 65. You don't know what you're talking about, and when someone calls you on it - like me or LoudThud - you get PO'd.

When I read someone posting misinformation, and continuing to argue incorrectly about it, I politely post the correct information. Your responses were out of turn. I've been an Electrical Engineer for 32 years, with 2 engineering degrees, 7 years of college and working on amps since 1966. I can *clearly* tell you do not grasp EE fundamentals. I think *you* need to learn a little humility, and maybe chill out with a Corona. ; )

[bnwitt]

You know corndawg, every degreed engineer I've ever met was a theoretical genious and a practical idiot. Those engineering degrees are famous for producing bridges that collapse, crippling space telescopes and creating other devices that kill millions. Yeah you guys are the best!! Would I go into battle with ya? Nah I don't think so.

You are all typically self impressed over educated jack asses who's egos and limited book learning empirical knowledge has gone to their heads convincing them that regurgitating what a professor says is better than field experience. Your classmates keep trying to tell us global warming is due to man. And only time will show how funny that really is. As I said, you are a sad little man. Now go back to your myopic focus working on some unimportant electronic project with RoHS compliant components and leave us to evaluate your 20 minute legacy. What's next, a new Dyson vacuum cleaner? Or something yet unimagined with LED's? Thanks for the laugh dude. Your type really crack me up.

"I've got a degree!!! Very funny. I'll bet you'd make a hilarious cabby. Your lack of respect for the field repairman that has to fix your engineering screw ups is classic. Thank you, Really. I have totally enjoyed the bearing of your pitiful "I spent so much time on my education it must be valuable and you will respect it damned you!!" soul in this thread. How much money do you make a year friend? Is it over $200K like me? Did you get your moneys worth on that schooling?

Oh, I am so in awe of your intelligence. Yuk yuk. Too Funny. Enzo amazes me (and I mean that sincerly in every way). You just make me laugh. But, damn you're pitiful. I hope your parents paid for your education and you didn't spend your own hard earned money on it. Talk about someone who needs to learn some humility since you apparently don't understand it. Jesus! Your last post is like you writing your own eulogy. 32 years, two degrees, 7 years of college......God you're funny and so full of yourself. I'm amazed you can spell humility. Have you considered taking your act on the road. Frickin' hilarious, your ego. Thanks for absolutely making my day. It's nice to know that there are dumb asses with multiple degrees out there. Muahh! I could kiss you for affirming my life choices.

Go ahead, post another response. I know you need the last word to lay your head on the pillow due to your personal insecurity. Go ahead......do it, you know you have to in order to justify your existence. I'm waiting......for another laugh. So damned funny! Come on Mr. Spock, thrill me with your Vulcan geek fan logic.

You should really consider copyrighting and syndicating your ignorant remarks. To laugh like this every day many folks would pay a monthly fee.

Ok, I've done all I can to encourage you to post yet another stupid diatribe for my entertainment by playing on your self doubt and self worth. Don't dissapoint me corn dawg. Fork over the fun. Give in to your personal weaknesses and spout some more crap for me to enjoy. Oh mighty college edumacated guru. God I love ya'. I'd dance at your wedding.

[dehughes]

So anyway, I was able to get my amp pretty darned quiet with those DC heaters. A lot of work, but well worth it. I noticed that the 2k5 resistor gets kinda hot, but I gave it space around it, so it should be fine. It's a tough RS-5 Dale, so I'm not worried.

So that took care of the hum...AND, I found that putting a 100pf cap across the plates of my PI took care of some of the frying-pan-skillet sizzle that would crop up from time to time. Now the amp is much quieter. Thanks to all.

However, I'm experiencing some midrange "edge" or "harshness". With my Tele (which has NEVER let me down through any amp...it's my benchmark guitar for testing out anything gear-related), on the bridge pickup, I'm noticing that there is this midrange quickness that just jumps out when playing stuff on the middle/upper strings on the middle/upper frets. It's like the amp is just reacting quickly and harshly in the midrange frequencies. Lows are KILLER, and highs are nice and airy, but the midrange just has an edge. It's not the speaker (G12H30....tried out different speakers and cabs....no change), and it's not the power tubes or their bias (352v plates, 300Rk on the 6V6 pair with 22v across the resistor....roughly Class A). That's the next thing to tackle...I'm looking at the PI, or how I have the channels coupled for ideas.

Here is what I have thusfar:

Channel 1: 6SN7, 115/118v per plate, 4-ish volts on the cathodes, 220k plate resistors with 2k7/25uf on the cathodes. Triodes run in series with a volume pot only (500k) in between.

Channel 2: 12AX7 - basically dead-on Brown Deluxe, 150-ish volts per plate, 220k plate resistor on first triode, 1k5/25uf and 2k7/25uf on the cathodes, 15k/100k plate resistor on second triode with a .01uf cap to the PI. Volume/tone in between the triodes, .01uf to ground on the tone (1M), with a 500pf to the volume (1M)

Channels mixed with 220k resistors into a .01uf cap and off to PI

PI: 12AX7 - 100k/100k plate resistors with 100pf across the plates, 1M grid resistors joining under a 1k2, which sits over a 47k to ground. .01 uf on the input side, .1uf on the unused grid side right to ground.

.1uf coupling caps into a Cut control (a la AC30) into 220k resistors from grids to ground, 1k5 resistors into 6V6 grids

Power Section: 6V6 pair, 300R/25uf on the cathodes, 352v on plates, 22v on cathode

Recto: 5AR4, about 360 off of the plates

As well, I noticed that when I have both channel volumes down, I still get the faintest guitar signal coming through the amp. I've never experienced this in other amps....any ideas?

I'll re-draw up the schematic now that I've made these changes, and post it ASAP. Thanks so much!