silvertone 1484 reverb(?)

[pontiacpete]

I really hate to beat this issue to death, having glanced through all the other threads on this amps reverb and realizing that it gets a very poor review, I can't even get this amp to produce the "crappy' sound that several of you have described.
I found that R45 27K was open and R46 had go high in value so I replaced them. When i first examined the reverb tank I noticed that the spring had come off, perhaps sometime before I got it or when I opened it, don't know.

What could have caused R45 to open up? Putting a new one doesn't get the crappy reverb going.
Nor did replacing C18 or C19.
All other resistors measure up close enough to the intended value.
I changed out the 2 tubes and found the original silvertone 6cg7 was weaker than the one had.
Changed the 12ax7 V4 with a stronger one.
All the voltages seem pretty close to practically spot on with the schematic.
No reverb.
The other question that comes to mind is this spring. The one that was in tack has these little card board pieces where they sit over the brass holder.
I cut some more from regular cardboard. Still no crappy reverb
I know it's probably not worth but I'd like to get it going.

thanks for any help.
pete

[Enzo]

WHy R45? Who knows? SHorted 6CG7? Age? Heat?


No reverb? Isolate the problem.

Every reverb has two ends - drive and recovery. WHich circuit is working and which not? Or both.

The return circuit goes to the grid pin 2 of the 12AX7. Also looks like it goes to the ring contact of the FS jack. In any case, pick a spot there and touch it with a small screwdriver or your meter probe. You get hum out the speaker? If so, it works.

The drive circuit is that push-pull thing driving a piezo element. You got signal coming through C18,19? If so, that works.

Now the crappy reverb thing itself. There is a long spring running its length - well not long as reverbs go. Then a little way in from each end is a piezo wafer wedged into a metal contact base. If that is what you are calling a cardboard square... then you replaced your piezo elements with cardboard.

Follow the wires up to the reverb, where do they connect to anything inside? Where they connect is where your piezo transducer goes.

[drewl]

FWIW I had one last week with really dirty tube sockets that would cause the reverb return amp to stop amplifying.

[pontiacpete]

Thanks Enzo,
Sounds like the piezo is the problem.

But just to double check I ran this test and it does hum on pin 2.

I put the scope on pin 6 of the 6cg7 where C19 connects and I have a signal.

So, cardboard won't work like a piezo, hmmm...
I'm trying to find a place to purchase this piezo wafer. Do you know of a source?

thank you very much for your help and time
pete

[Enzo]

I have made them, but it is a pain in the ass. The original ones were plain two sided piezo wafers. In other words a ceramic disc with conductive layer on each side. Look at the little clamp that holds them. Wedge the piezo in there and each side of hte clamp makes contact with one side of the disc. If you can find piezo discs like that, great.

What I had to use was the wafer from a piezo tweeter - like the kind in all the cheap PA speakers in the world. Unfortunately, those are a sandwich. There is an internal conductive disc - brass maybe? and a layer of piezo crystal on either side of it. Thent he exterior sides of all this have a conductive layer. The two outer layers are jumpered together from one side to the other. SO to use it, I had to modify the mounting clamp to make contact with the outer layer and get a wire to the inner layer. Just shoving the wafer in the existing arrangement winds uop shorting across it because the two outer sides of my piezo are wired together. Follow?

The wafer disc in the tweeter is way too large and round, so I had to break it to get the size and shape. I don;t really care if the shape is odd, all it has to do is stick up into the long spring and get vibrated.

Other alternatives? I am sure they are out there. Look for piezo elements in the hobby market.

[pontiacpete]

What I had to use was the wafer from a piezo tweeter - like the kind in all the cheap PA speakers in the world. Unfortunately, those are a sandwich. There is an internal conductive disc - brass maybe? and a layer of piezo crystal on either side of it. Thent he exterior sides of all this have a conductive layer. The two outer layers are jumpered together from one side to the other. SO to use it, I had to modify the mounting clamp to make contact with the outer layer and get a wire to the inner layer. Just shoving the wafer in the existing arrangement winds uop shorting across it because the two outer sides of my piezo are wired together. Follow?


.

yes, thanks, I'm going to look into it.
thanks!
pete

[melvin]

It may be possible to convert the crappy twin twelve reverb into one of the best reverbs put in a guitar amp. It seems the Ampeg VT-22 used the same compliment of tubes for drive and recovery of the reverb. If the Ampeg pan, which is a high impedance accutronics reverb tank, will fit inside that tiny little box (or perhaps in a bag on top), it may work... If the twin twelve's power supply can handle the changes you will need to make to the driver configuration, it would have one of the best reverbs as well as already one of the best tremelo's out there.... What do you guys think?

[duffy878]

I'd love to have that Ampeg reverb in my 1484. I got mine without the POS piezo tank and I most certainly will not be hunting for one.

anyone have a good VT-22 schematic?

[Amp Kat]

The Free Information Society - Ampeg VT22 Electronic Circuit Schematic

[Dave Curtis, dB AudioTech]

This one has better resolution.

[duffy878]

okay so I redrew the reverb section of the vt-22 that you'd have to build into the 1484. I didn't change any values so if any are different, they're a typo and you should tell me so I can correct it.

The only thing that would need to be figured out is the values of the resistors with the question marks in order to get the voltage at the plates what it should be. The necessary voltage (as given on the VT-22 schem) is in red.

I believe the 'IN' would be PIN 7 of V2 (connected to the wiper of R21)

I'm not sure on where the 'OUT' would be connected.

[25orsixtwofour]

sooo...

i'm hoping to get the serial for a replacement tank for a 1484, the reverb really is awful, anyone end up taking this all the way?

[duffy878]

after thinking about it for a while I came to the conclusion that its just not worth the hassle and I bought a reverb pedal instead. works for me.