Amp build for a first time builder?

[martin manning]

All my schemos show 320uF

'57 Fender schematic...

[guitardude57]

oops, mine was a Marshall...

[yoyohomieg5432]

well another capacitor i seem to not have is the 10uF 450 V.. kind of disappointed with how many things seem to be missing.

i'll take a picture of what i've done today in a minute. i had one issue with one of the resistors, the 100k had to be on an angle and it really isn't very long so i just kind of had to rest it on top of the eyelet and load it with solder.. i hope it will hold. if not i may have to solder a short wire to it to lengthen it.

[yoyohomieg5432]

ok, here's what i've got so far..

- i haven't added the green wires for v1a g, etc.. i didn't solder those locations yet

-2 locations that are missing capacitors

-Martin, you may notice I added a few eyelets to the left side that I haven't soldered yet. the eyelets were rather short, so they went through the board but when i used a screw driver to flatten them out, there wasn't much metal to flatten out. they seem to be relatively sturdy but i'll have to make sure i get a good connection with those for sure.

[martin manning]

ok, here's what i've got so far..

- i haven't added the green wires for v1a g, etc.. i didn't solder those locations yet

-2 locations that are missing capacitors

-Martin, you may notice I added a few eyelets to the left side that I haven't soldered yet. the eyelets were rather short, so they went through the board but when i used a screw driver to flatten them out, there wasn't much metal to flatten out. they seem to be relatively sturdy but i'll have to make sure i get a good connection with those for sure.

I think you said before that there were some parts back-ordered from Mojo, wasn't that V1 cathode cap one of them?

On the eyelets, I'm not sure what you mean by "flattening" them; they should be flared on the back side like (probably) the ones that were already installed. A screwdriver wouldn't be my first choice... maybe you used a Phillips head driver? The tool I use is from a craft store, but it is just a steel rod with a ~45-degree conical point. As I suggected, a center punch would do nicely if you have one. The connection won't be an issue, but you want the eyelet to be securely attached to the board. Your picture doesn't have high enough resolution for me to see what they look like in detail.

Component leads have gotten shorter since the '50's and '60's when point-to-point wiring gave way to PCB construction. What you can do with that resistor is put a right-hand bend in the lead that won't reach and hook it around the resistor lead to its right. See below...

I would not bend so much component lead over on the underside of the board. In addition to using up lead length, it will make the parts very dificult to remove if you find yourself wanting to tweak values or replace them.

[yoyohomieg5432]

ok, here's what i've got so far..

- i haven't added the green wires for v1a g, etc.. i didn't solder those locations yet

-2 locations that are missing capacitors

-Martin, you may notice I added a few eyelets to the left side that I haven't soldered yet. the eyelets were rather short, so they went through the board but when i used a screw driver to flatten them out, there wasn't much metal to flatten out. they seem to be relatively sturdy but i'll have to make sure i get a good connection with those for sure.

I think you said before that there were some parts back-ordered from Mojo, wasn't that V1 cathode cap one of them?

On the eyelets, I'm not sure what you mean by "flattening" them; they should be flared on the back side like (probably) the ones that were already installed. A screwdriver wouldn't be my first choice... maybe you used a Phillips head driver? The tool I use is from a craft store, but it is just a steel rod with a ~45-degree conical point. As I suggected, a center punch would do nicely if you have one. The connection won't be an issue, but you want the eyelet to be securely attached to the board. Your picture doesn't have high enough resolution for me to see what they look like in detail.

Component leads have gotten shorter since the '50's and '60's when point-to-point wiring gave way to PCB construction. What you can do with that resistor is put a right-hand bend in the lead that won't reach and hook it around the resistor lead to its right. See below...

I would not bend so much component lead over on the underside of the board. In addition to using up lead length, it will make the parts very dificult to remove if you find yourself wanting to tweak values or replace them.

I'm pretty sure the backordered parts are different from the capacitors I was looking for yesterday. I checked yesterday but I'll check again when I work on it today.

As far as the eyelets go, I did use a center punch on them as well. They feel like they are secured well but as I said these eyelets weren't very long so I didn't have much length on the other side of the board to flatten.

I will trim off some more wire I just didn't have a wire cutter handy.

I like your idea with the resistor. I'm assuming I should still solder it in place, right?

[martin manning]

I'm assuming I should still solder it in place, right?

Absolutely!

[yoyohomieg5432]

that 6.8k resistor towards the center of the circuit board was a mouser part right? why are we using this one instead of the original 10k?

i also can't find the 470 ohm resistor :/ another part i need to get..

[martin manning]

Recall I explained that the Fender schematic is from '57. The '59 production examples have a couple of changes. That PI tail resistor is one, and the others are the 100k vs. 56k "slope" resistor and the 0.1 vs. 0.02 Bass cap.

Wasn't the bag with the stomp switch in it marked 470R? Those won't be hard to find locally.

[yoyohomieg5432]

i'm going to place another mouser order with everything i need now. i was hoping you could check through these and approve/give other suggestions. there are a lot to choose from.

-any advice on the 470 ohm resistor? What power rating? Martin you made a good point about that bag with the foot stomp switches. That bag said 470 ohm 1W. I'm thinking I should get 1W. What tolerance?

-1x 220uF 50V cap:
http://www.mouser.com/ProductDetail/Kem ... wXFOgcw%3d

-1x 10uF 450V cap:
http://www.mouser.com/ProductDetail/Nic ... 5rN0fhs%3d

-1x 47pF 500V cap (the mojotone bag says silver mica 47pF 500V)
http://www.mouser.com/ProductDetail/Cor ... %252bng%3d

-1x 250uF 25V (the mojotone bag says TAD 250uF 25V bipolar)
http://www.mouser.com/ProductDetail/Vis ... lGVXLC8%3d

-250k linear pot for treble. again, not sure on tolerance/power rating
http://www.mouser.com/ProductDetail/Bou ... pdwz8gI%3d

-5k linear potentiometer.
i cannot seem to find one that looks like the other potentiometers. i can find one easy on mojo but don't want to shop there http://www.mojotone.com/amp-parts/poten ... Nt3RHenmuI

[yoyohomieg5432]

another update:
-i just got an email about those 27k resistors from mouser.... they aren't expected to ship until march. how about this one instead: http://www.mouser.com/ProductDetail/KOA ... 252bxk4%3d

-i'm almost done with soldering the board. i'll take a pic later. a little concerned with the bourns trimmer. the legs are pretty short, one of them was not going into the eyelet very well but i loaded it with a good amount of solder and it looks like it will hold.

[martin manning]

Here are some better part numbers for the 220uF @35V 647-TVX1V221MAD and 10uF @450V 647-TVX2W100MCD You listed two 220uF, but you only need one. An ordinary electrolytic is fine there, no need for a bi-polar.

The silver Mica you selected is fine, and so is the 27k resistor.

On the 470 ohm, there are three of that value. One is the bias resistor in the phase inverter, where a 1/2 watt is big enough. The other two are the screen grid resistors, which were spec'ed at 1W in the original schematic, and are mounted on the power tube sockets. Most people use higher wattage there, often 5W cement-filled ceramic, so they can stand a power tube short. Here's a 3W 5% part that will be good for that use and is a bit smaller in size: 594-AC03W470R0J .

What you want for the pots is a 1" (or 24mm) case with solder lugs, a 3/8" bushing (for the 3/8" chassis hole), and a 1/4" solid shaft. Mouser doesn't have anything like that that I can see. I usually get pots from a specialist supplier like Antique Electronic Supply or Triode, but paying for shipping two pots seems silly. I would say go ahead and use the ones you have, and if you really hate the functionality you can always change them later.

[yoyohomieg5432]

Here are some better part numbers for the 220uF @35V 647-TVX1V221MAD and 10uF @450V 647-TVX2W100MCD You listed two 220uF, but you only need one. An ordinary electrolytic is fine there, no need for a bi-polar.

The silver Mica you selected is fine, and so is the 27k resistor.

On the 470 ohm, there are three of that value. One is the bias resistor in the phase inverter, where a 1/2 watt is big enough. The other two are the screen grid resistors, which were spec'ed at 1W in the original schematic, and are mounted on the power tube sockets. Most people use higher wattage there, often 5W cement-filled ceramic, so they can stand a power tube short. Here's a 3W 5% part that will be good for that use and is a bit smaller in size: 594-AC03W470R0J .

What you want for the pots is a 1" (or 24mm) case with solder lugs, a 3/8" bushing (for the 3/8" chassis hole), and a 1/4" solid shaft. Mouser doesn't have anything like that that I can see. I usually get pots from a specialist supplier like Antique Electronic Supply or Triode, but paying for shipping two pots seems silly. I would say go ahead and use the ones you have, and if you really hate the functionality you can always change them later.

do you think radioshack would have the pots i need?

also, you're saying to get two 220uF 35V? Why? One place calls for a 220 but 50V rating and the other calls for a 250uF and 25V rating. Does that extra 30uF not matter? Or were both of these caps meant to be used at the same place?

a few other questions:

1) 1R1% on the 5881s is the 1ohm resistor for measuring the current right?
2) there's a .05uF 600V cap on the schematic but I don't see it in the mouser order spreadsheet or the mojo order. should i get one of these too?
3) on the bright volume pot there's something htat says 100MMF.. what is that?
4) the schematic shows a 4k7 2W, but mojo includes a 4k7 3W. that shouldn't matter , right?

[martin manning]

do you think radioshack would have the pots i need?

Not likely at all.

also, you're saying to get two 220uF 35V? Why? One place calls for a 220 but 50V rating and the other calls for a 250uF and 25V rating. Does that extra 30uF not matter? Or were both of these caps meant to be used at the same place?

There's only one low-voltage 200-ish uF cap in the circuit, bypassing the cathode resistor at V1. A 220uF is effectively the same as a 250uF, and is now the more-or-less standard value. That cap doesn't see more than a few volts, so the rating isn't critical. A lower voltage cap will likely be a bit smaller, though.

[martin manning]

a few other questions:

1) what is 1R1% on the 5881s?
2) there's a .05uF 600V cap on the schematic but I don't see it in the mouser order spreadsheet or the mojo order. should i get one of these too?
3) on the bright volume pot there's something htat says 100MMF.. what is that?
4) the schematic shows a 4k7 2W, but mojo includes a 4k7 3W. that shouldn't matter , right?

1) 1 ohm, 1% tolerance. These are the current sensing resistors for setting bias.
2) That cap (shown on the layout) is across the standby switch to help suppress arcing. It's not absolutely necessary, but you can put one there if you like. The original 5F6-A layout shows a 0.05uF from the standby switch to ground. Thinking that one of those might be included in the Mojo parts kit, I moved it across the standby switch.
3) MMF is old-school notation for pF. It stands for micro-micro Farads.
4) 3W is fine for the 4k7.