Dual Channel 5F10 - first amp, build journal

[smithcircuits]

Ok, so I just ordered a cab and chassis from weber for my first amp build. The plan is a tweed harvard 5f10 in a 5e3 cab & chassis, utilising the extra triode of a 5751 with a split cathode in V1 for a "lead channel" as per the rob robinette 5e3 mod. Also adding a bias pot, variable negative feeback control, and a reduced tone cap. A buddy of mine has an unused g12h30 laying around, so I'm thinking for free that'll do just fine as a speaker compliment.

I'd really like some input from more experienced builders before I order the rest of the parts. My main concern, other than potential fatal flaws in my wiring scheme here and the build plan generally, is the 330-0-330 secondary on the 290BX playing ball with this circuit and a 5y3... this thread seems to be a proof of concept for the application. Am I in good shape here?

Hoping to lean on this community as the build gets under way, so any input is greatly appreciated. I've been doing a lot of reading, but I'm green, so go easy on me!

 

[2L man]

Separate cathode circuits for input tube make sound more versatile!

You should Install 1 ohm cathode resistors for power tubes and monitoring tube bias, balance and "health" is easy.
Also Install 68k input resistors to control grids and they function better and save room from circuit board.
A Single ground bus 0VDC for all HV return current back to PT CT is easy and function best.
High voltage fuse between rectifier output and B+1 can save Output Transformer and/or rectifier tube some day and guitarist life as well.
Silicon diodes to rectifier tube anodes is also good safety/reliability practice.
"Elevated filament" is efficient hum eliminating method. Installing two resistor voltage divider to HV/0VDC and connecting filament CT there elevate enough. It also bleed the electrolytes. 270k/56k is one option.

 

[printer2]

All that 2L has suggested, not sure if you want the bias pot on the back panel if you need to measure the current by removing the chassis (unless you will be using a Bias Rite). If you will be going with the 1 ohm resistors, a pair pin jacks to check bias, then the back panel mounting would be convenient.

 

[smithcircuits]

Brilliant!

 

[NTC]

I'd really like some input from more experienced builders before I order the rest of the parts. My main concern, other than potential fatal flaws in my wiring scheme here and the build plan generally, is the 330-0-330 secondary on the 290BX playing ball with this circuit and a 5y3... this thread seems to be a proof of concept for the application. Am I in good shape here?

I have a 5F11 (Basically the same as a 5F10 but with Trem) in a 5E3 chassis and a 290BX. With the 5Y3 and the output tubes biased at 70% or slightly less, I am getting 422V on the plates of the 6V6's when the wall voltage is 121Vac. It is a bit high - more like an AA864 Princeton (non-reverb - also a very similar amp). It was VERY clean with the stock feedback resistor. The feedback control will probably be your friend here.

 

[smithcircuits]

I have a 5F11 (Basically the same as a 5F10 but with Trem) in a 5E3 chassis and a 290BX. With the 5Y3 and the output tubes biased at 70% or slightly less, I am getting 422V on the plates of the 6V6's when the wall voltage is 121Vac. It is a bit high - more like an AA864 Princeton (non-reverb - also a very similar amp). It was VERY clean with the stock feedback resistor. The feedback control will probably be your friend here.

That's what I like to hear! Thanks!

 

[David Barnett]

So it's a Tweedle Dee with fixed bias?

The G12H30 Anniversary is a great speaker, almost any amp will sound good through it. It's warm but articulate.

 

[2L man]

All that 2L has suggested, not sure if you want the bias pot on the back panel if you need to measure the current by removing the chassis (unless you will be using a Bias Rite). If you will be going with the 1 ohm resistors, a pair pin jacks to check bias, then the back panel mounting would be convenient.

Yes, those are pro-way to do bias measures! Also 2,1mm plugs (pedal board standard) work and two females are needed. Then male plug/cable which other end has banana sockets for multimeter.

 

[smithcircuits]

Incorporating a some of these suggestions. The 290BX doesn't have a filement center tap, so I'm following rob robinette's lead on making an artificial center tap to ground the heater tap. Is this kosher? Do the test points (red and black eyelets) mess with the artificial heater center tap? I have the two 100R resistors going to ground through the bias test point resistor...

Mine:

Rob's:

 

[smithcircuits]

Ok, the parts are ordered and Weber says no later than 5 weeks for the cab to ship! The cab's gonna have a tv front, black tolex, and bluesbreaker-style pinstripe grille cloth. Weber said they'd add some white piping around the grille cloth for me too. Really going for style points here lol

Not your grampa's 50's tweed

 

[Uffepungen]

Very cool project! Can't wait to follow this along

Also, good choice on the TV front, they are so cool.

 

[smithcircuits]

Updated layout

 

[smithcircuits]

Alright, we're getting somewhere... wired up the brain & drilled for some test points and holes for mounting the board.

Had to place another order for some nuts & lock washers I forgot about & a switch for the negative feedback control - didn't think about how the chassis hole for the standby switch that I intended to use would be too big for a potentiometer lol. So nfb will be a three way switch instead with standard, lower & lowest negative feedback settings at 22, 55 & 90k values in sum.

Feeling optimistic so far!

 

[Liriodendron]

Looking good. Any reason you soldered the comps in the eyelets before wires?


I don't use eyelets much, but when I do, I typically just lace the comps, and leave the leads long on the back until I stick wires in there, then I solder the whole deal. Then I'll clean up the long comp leads with some nippers. My process is to completely wire the board, except for any AC wiring that is attached to transformers and the like, before I put it in the amp. Then I simply trim wires and connect leads to sockets, pots and switches. To aid in my sanity, even on small amps, I use different colors for B+ leads (typically red), ground (black), grid and signal (blue or white), plates (orange or red), cathodes (yellow or white) and heaters (green and white).

Maybe that helps... good luck!

 

[smithcircuits]

Oh, yea... that would have been the smart way to do it lol. I'm waiting on some wire to ship too and I guess I was anxious to get the board populated. So far the eyelets are forgiving but some of these will have 4 wires in one hole which will be a bit of a squeeze. I think I can make it work thanks!

 

[Liriodendron]

Sometimes it can be tough to get 4 in, especially with solder. What I do is hold the iron on there and poke it in while it's hot. Works a lot better with solid core wire. Stranded can be tricky.

 

[smithcircuits]

Edit - nvm, dumb question.

 

[gabasa]

Nice work so far, I always thought a tweed Deluxe with Harvard tweaks would be a cool amp, but I've never tried it. Which OT are you using? i think that a 125A1A style of OT with 6.6k primary would rock, but YMMV.

 

[smithcircuits]

Thanks! Parts are all in now (except the cab) so wiring is imminent. I have a 1750E for the OT. Not sure now if this is more a deluxe w/ harvard tweaks or a harvard w/ deluxe tweaks? lol

 

[smithcircuits]

ok all wired up. trying not to feel too pleased with myself until I know it works gotta go pickup a new multimeter and then to run some tests.

it's all a bit more cramped than I expected, but no major challenges.

fingers crossed!