Silvertone 1484 tube loop
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ok_state_blues
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Silvertone 1484 tube loop
I am needing some advice on the possibility of making the reverb loop in a silvertone 1484 into a tube buffered effects loop. As many know the reverb in these amps is not great, usually D.O.A., and less than desireable to most ears. My question is, based on the schematic could I delete the reverb circuit and rewire the socket to be a tube buffered effects loop? Based on where the current reverb cicuit sits, it seems a prime place to upgrade. The attached example is one that is from Dan Torres' book. If anyone knows of a better one, I'm all ears.
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Re: Silvertone 1484 tube loop
Doesn't seem like a great idea. The depicted circuit appears to pick off of a leg of a phase inverter. I don't know what you're looking to drive externally, so need to get the levels and loads of what you're going to loop in and out of defined first.
I was able to get the existing piezo reverb working pretty well in mine, the secret everyone seems to miss is to tie down the spring in the middle. The failure mode is the thread breaks, the spring is then unrestrained, bounces all over the place in transport and knocks itself and the paper insulators off the piezo disks on the ends. When you get the thread tension just right, the reverb is not half bad. Certainly not in deep Fender territory, but surprisingly decent. Might give it a shot to see if you can fix it first and at least know how you feel about it.
If you want to add an external effects loop, the makings of it are already there. The reverb has two tubes, a 12AX7 and a 6CG7. The 6CG7 is operating as a paraphase inverter, and drives the piezo in the tank. It makes about 50v-90v peak-to-peak in order to drive the spring. (the tank is bidirectional, piezo is the same on either side).
Each section of V4, 12AX7 is used. First triode section, pins 6,7,8 take the preamp signal and boost it to feed the paraphase inverter. The "Rev Depth" control is like the "Dwell" control on a Fender reverb unit, it controls how hard the drive into the spring is.
The second triode, pins 1, 2, 3, are the recovery amplifier, which takes the return from tank and amplifies it, unlike typical Fender reverb amps, there's no control of the return level. The signal is mixed in at the plates of V2 (both channels) and into the first section of V3.
If one were inclined to implement an effects loop, you almost have one there at V4. Could simply delete V5 and its associated components. Then convert the V4 stage into a cathode follower, go out from there, and use the second section as the return buffer. With just a little re-implementing, you can implement the loop.
I think the Dumbleator circuit would work really well built around V4. Just scale the resistors to get the proper amount of gain and you're there.
But have a go at getting the reverb working, just for fun's sake if possible.
I was able to get the existing piezo reverb working pretty well in mine, the secret everyone seems to miss is to tie down the spring in the middle. The failure mode is the thread breaks, the spring is then unrestrained, bounces all over the place in transport and knocks itself and the paper insulators off the piezo disks on the ends. When you get the thread tension just right, the reverb is not half bad. Certainly not in deep Fender territory, but surprisingly decent. Might give it a shot to see if you can fix it first and at least know how you feel about it.
If you want to add an external effects loop, the makings of it are already there. The reverb has two tubes, a 12AX7 and a 6CG7. The 6CG7 is operating as a paraphase inverter, and drives the piezo in the tank. It makes about 50v-90v peak-to-peak in order to drive the spring. (the tank is bidirectional, piezo is the same on either side).
Each section of V4, 12AX7 is used. First triode section, pins 6,7,8 take the preamp signal and boost it to feed the paraphase inverter. The "Rev Depth" control is like the "Dwell" control on a Fender reverb unit, it controls how hard the drive into the spring is.
The second triode, pins 1, 2, 3, are the recovery amplifier, which takes the return from tank and amplifies it, unlike typical Fender reverb amps, there's no control of the return level. The signal is mixed in at the plates of V2 (both channels) and into the first section of V3.
If one were inclined to implement an effects loop, you almost have one there at V4. Could simply delete V5 and its associated components. Then convert the V4 stage into a cathode follower, go out from there, and use the second section as the return buffer. With just a little re-implementing, you can implement the loop.
I think the Dumbleator circuit would work really well built around V4. Just scale the resistors to get the proper amount of gain and you're there.
But have a go at getting the reverb working, just for fun's sake if possible.
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ok_state_blues
- Posts: 13
- Joined: Wed Mar 03, 2021 3:42 am
Re: Silvertone 1484 tube loop
Very encouraging. I'll do some poking around. Thanks for the insight!
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ok_state_blues
- Posts: 13
- Joined: Wed Mar 03, 2021 3:42 am
Re: Silvertone 1484 tube loop
@Nuke i took your advice and was able to get the reverb working on one of my 1484s. Happiness ensued. Then I moved on to the next two and even after taking your advice, when engaging the reverb, I just hear my guitar tone amplified into the reverb box. I.E. no reverb flavored guitar out of speaker. So on to reworking this part of the amp. Both channels work but reverb has no effect. Would anyone have a suggestion on how to install the D_mble type loop in its place based on the schematic? Or maybe change it to Merlin's Practical Serial Effects Loop as done by @Xtian?
Re: Silvertone 1484 tube loop
Let me ponder it a bit, and I'll see what I can figure out.
Are the reverb spring units on the other 1484's toast?
Are the reverb spring units on the other 1484's toast?
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ok_state_blues
- Posts: 13
- Joined: Wed Mar 03, 2021 3:42 am
Re: Silvertone 1484 tube loop
The 3rd makes no sound even through the spring like the 2nd. My thought is I could pull the reverb 6CG7 and wire the 12AX7 as a tube buffered effects loop. But I am open to suggestions.
Re: Silvertone 1484 tube loop
I haven't forgot about you... just need a chance to draw up a schematic and summarize my thoughts.