Silvertone 1472 Mod Help

[SDS]

Hey folks... long-time/first-time,

I'm looking at modding a stock Silvertone 1472. The changes I want to make:

1. 2 -> 3 prong conversion
2. Re-cap and test resistors
3. Permanently jumper the mic & inst channels
4. Drop the tone stacks (amp is more than dark enough already)
5. Possibly drop the infamous "TREMLO" circuit (their typo, not mine). I've got an Airline 62-9023... If I need tremolo, it's one of the best there is.
7. Combine the volume control for the two channels on one volume knob.
8. Chop down the chassis to shrink the footprint and pop the head into a new frame

This is not my first project but it's been a while since my last ones and to spare you having to serve the obligatory warning and let you know that charged capacitors scare the s%*t out of me.

Here's a link to a schematic:
http://www.prowessamplifiers.com/schema ... ne1472.pdf

Mods # 1, 2, and 3 are easy and I have the info I need for them. But if you have any hot tips (favourite cap type/brand), send them my way!

Dropping the tone stacks - is this as simple as cutting out C4, C5, R9, and R10?

Dropping the Tremolo - is this as simple as:
a. cutting the connection that originates between R21 & R22 that runs to the tremolo footswitch jack, AND
b. cutting the connection from pin 4 of the 6V6's before it reaches R30, R31, and C13?

Considering I'm taking a tube out of the circuit, I'm assuming would then require changes to the power section, yes? If so, It might not be worth doing. I'm looking for audible mods, not power mods (other than the 3 prong). I'll save the power section mods for another project.

Combining the volume knobs - yeah, I need help on this one. How do I do this?

Thanks in advance for your help.

-Scott

[xtian]

I'm about to tackle items 3 and 7. Going to adapt the 1482 circuit to fit into a combo.

Yes, dropping the tone stack is as easy as you say. But if you find your amp too dark, this won't help. You should add a bright cap, 50-500p across the input and wiper of the volume pot.

I'm going to leave one of the input triodes stock, with 2k2/330k resistors, and put the other triode to Fender stock, 1k5/100k, and leave both volume controls so I can mix the channels like a jumpered plexi.

[SDS]

Thanks xtian!

Thanks for the confirmation. I realize that dropping the tone circuit won't brighten things. I'm not ready to brighten up the tone (yet) but I know that I don't have much desire to make the amp any darker... so, might as well lose the unnecessary parts. The channel blending is cool but I want a stripped down, no options tone machine and the 1472 is a great starting point.

[SDS]

Can anyone chime in regarding the tremolo or combining the 2 volume knobs into 1?

[xtian]

Dropping the Tremolo - is this as simple as:
a. cutting the connection that originates between R21 & R22 that runs to the tremolo footswitch jack

You need to take the wire from the junction of R21 and R22 and ground it. Just like when the tremolo footswitch is closed.

b. cutting the connection from pin 4 of the 6V6's before it reaches R30, R31, and C13?

Yes.

And for the volume, just move it to the point after the two 330K mixing resistors (R13 and 14). The volume control will just serve to ground the input of the next stage.

[SDS]

6 knobs down to 1...

I like it.

Thanks xtian!

[SDS]

Okay folks,

I've been chipping away at the schematic for the changes I want to make and I think I'm ready for feedback.

xtian - I liked your idea for the 1 channel of Fender style 1.5k/100k so I 'borrowed' it. I'll have to play with the mixer resistor values to get the right blend of course but for now we'll just assume that 50/50 will work out perfect.

And yes, the 500pF bright cap is high but I'll start there and bring it down as needed.

Any advice?

[xtian]

C1 and R15 look wrong. R15 looks like it should be another dropping resistor in your power string (like 15K), and C1 would then be the last filter cap, like 8u.

I'd replace your mixer resistors R13 and 14 with volume pots so you can mix the two inputs. Move your bright cap off the input and onto one of these two volume pots, and you'll have some tone control just by mixing channels to taste.

[SDS]

Thanks xtian!

... But I'm a little confused - C1 and R15 are in the same location and have the same values as the original schematic. Maybe they need to be changed because of other changes I have made, but if that's the case can you please explain what I did to require the change?

As for the bright cap... all I can say is I need sleep. I wanted that to be on the existing pot (R11).

I get why using pots for R13 & R14 will be handy and I will likely install them temporarily to find the values I want, then replace them with hardwired resistors. If you can't tell, I like limitations... tone is in the hands after all ! Question is: what is the safe range of values I can use? Will going too low or too high with the resistance damage components downstream?

New schem with bright cap on volume pot.

[xtian]

You're right about the original schematic. Sorry, I didn't look. I'm not familiar with this unusual config.

Your bright cap should connect from the wiper of the vol pot to the input of the vol pot. But I can tell you you'll want to switch it out.

Now that I review the 1472, I say leave the pair of 330K mixers as they have, and implement the two vol pots as shown.

[SDS]

New question for this (re)build:

I'm thinking the pentode/triode switch is going to get me where I want to go - lower output and mid-driven tone. Although I don't actually want a switch... just to leave it in triode mode.

Not sure how to implement it on this amp though because from everything I've read there needs to be screen resistors off pin 4 before you connect back to pin 3. Currently this amp doesn't seem to have screen resistors for the 6V6's but can I just add some 1k 2-5 Watt resistors between pin 4 and pin 3?