Blues Amp Build

[Pdavis68]

I'm about to start breadboarding my blues amp build. Again, going for the ghetto amp style, this time using a cake pan, which ought to offer me a lot more room to work.

I'm going to go with either 4 or 5 tubes (I only have 4 sockets in right now, but I'm probably going to put a 5th in so I can add reverb). My question is about the heater wiring. See the attached photo.

The sockets are very close together. Is it sufficient to run the heater wiring from socket to socket directly without running it to the corner of the chassis between tubes? Seems to me it would add a lot of unnecessary length to the wiring to run it to the corner.

[DRH1958]

You could elevate the heater wires as in the attached photo like the orange/yellow twisted pair. That octal socket might be a little close to that 9 pin.

[Pdavis68]

Okay, that's what I thought I could do. Thanks.

I was actually thinking that about the spacing as soon as I started punching the 9 pin hole (which would have been a super time to stop and rethink it, but as I have $1 invested in that cake pan/chassis, it won't be a major loss if I have to toss it). Will it be a problem having them that close? Is it something a tube shield can fix?

[DRH1958]

I have a great book by Morgan Jones on the actual physical construction of amps and he recommends power tubes be spaced 1.5 times the diameter of the tubes from preamp tubes. It's more about heat transfer from the hotter tubes to the preamp tubes and not necessarily interference. He doesn't mention shielding as a fix for this. He also recommends this spacing between power tubes if there is more than one.

[Pdavis68]

Ah, I see. So it's a heat issue. Hadn't considered that. It's going to be an SE amp, so only one power tube. It ought not get too bad, though in the future, I'll be better about spacing.

This amp is actually a bit of a test run anyway. I have a buddy who is going to want one similar to this, so I'm building one for myself first to get the kinks out. If it becomes and issue I could just erect an upright metal plate between the power tube and that first preamp tube to act as a heat shield. I'm building it in a cake pan, so obviously I'm going for function before beauty...

[Leo_Gnardo]

More things to think about whilst you're still in planning stage: hum from single ended output. Champs are (in)famous for this. It may or may not be an issue for you, but if you're interested in a low noise floor for recording or just not being annoyed by hum, there's a remedy & another poster has a thread going now about his 5F1 where some suggestions have been made to minimize it. Granted our OP there is distracted with some irrelevancies & dodgy "science". I'm sure you'll be able to tell the sheep from the goats, and perhaps improve your amp thereby. Useful stuff starts about post #12 and ends at #28:

http://music-electronics-forum.com/t40815/

Don't burn that cake!

[Pdavis68]

Thanks for that, Leo. So, I think the takeaway is that a CL filter before the first B+ node might save me some hum... I was actually strongly considering going with a choke for this build (I didn't on my SE Valve Jr build and it does have some hum when cranked). I was just going to get one and try it out and see what effect it had. I'll try it out on the breadboard and see if it helps.

[Enzo]

CL or even just a CR, but an extra filter stage before the first node.

[Leo_Gnardo]

Of course other hum sources need to be minimized, keeping filament leads away from preamp control grids, placement of OT wrt PT, like that. This "pre filter" does away with the hum that's there no matter where you dial your controls in SE amps, due to no handy hum-cancelling via output transformer as found in push pull circuits.

[Enzo]

Yes, hum is a whole science in itself.

[elipsey]

I put a choke in my 5f2a and was amazed at how quiet it was. Discussed here: http://music-electronics-forum.com/t36424/

DRH, is that picture a princeton reverb clone? Looks pretty familiar....

[Pdavis68]

Well, I definitely want this to be a quiet amp (particularly the one I'm building for my friend), so I'll probably go with LC, but I'll try RC as well.

And yes, Leo, I didn't figure this would fix all sources of noise. I'll try DRH's heater wiring through the air thing.

For my buddy's, I'm going to use a real chassis and I won't put the tubes so close together, so I'll probably wire that one up in the more traditional fashion.

[DRH1958]

DRH, is that picture a princeton reverb clone? Looks pretty familiar....

Actually I found that shot from Frugal Amps page on a Dumble style clone; Frugal Amps He's got a lot of great ideas.

[Leo_Gnardo]

Well, I definitely want this to be a quiet amp (particularly the one I'm building for my friend), so I'll probably go with LC, but I'll try RC as well.

Of course a resistor's a lot cheaper and smaller than a choke. OTOH what concerns me, is by the time you have a resistor that effectively quashes hum in the pi filter, you reduce B+ to the point it takes a serious bite out of the amp's power. This may or may not be a factor, depending on whether you think it's important or not.

And yes, Leo, I didn't figure this would fix all sources of noise.

As Enzo reminds us, and properly so.

For those who have hummy amps be prepared to answer the often heard question "why does your amp hum so much?"

"It forgot the words."

Note brand name on amp in foreground of this terrific album's cover art. Amps that buzz always remind me of this. The music is excellent too, in its own unique way, psycho-folk of the 70's. Recommended listening!

[Mick Bailey]

Is it sufficient to run the heater wiring from socket to socket directly without running it to the corner of the chassis between tubes?

Think about most PCB amps and that's exactly what you get. If you're lucky you may get some supplementary actual wire, and sometimes even twisted. But most of the time just parallel PCB traces. So you're in an improved situation anyhow.