Revisiting Sears Silvertone 1484/85 Piezo Tanks.

[DummyLoad]

From a thread from many years ago: https://el34world.com/Forum/index.php?topic=9951.msg93741#msg93741


Did my own take on the issue. My amp is a model 1484; mods should work on model 1485 as well.   


Moved the reverb signal source from the top of the ch2 volume to the wiper since, IMO, the reverb sounded a bit too thick at lower playing volume with mods.
Remove the paraphase divider network R47 & R48 & parallel the 6CG7/6FQ7 driver triodes; add a 10uF bypass cap to driver cathodes; replaced the pair of 27K plate Rs, R45 & R46 with single 15K 2W part; 3W/5W part is best there; 2W is what I had in stock and works for now.
Removed R40, 560K divider, replaced R41 68K with 220K (my amp had a 150K for R41).
I used a 8FB type tank; going to test with a type 4FB, I like the tone a bit better of the long tanks.
Plan to use a TRS 1/4" female jack to chassis and use a 1/4" male TRS to RCA jack splitter and mount the reverb tank in the speaker cab, right now tanks is connected with modified RCA patch cords with test clips.


Sounds really nice, much like the verb of my Ampeg VT40.

Link to schematic I used.

Link to schema of mods.


--Pete

[passaloutre]

Very glad to see this work done. The original Silvertone reverb tanks obviously being a weak spot. I wonder if one of those blue plastic tanks I see in pedals would work to fit it inside the original amp head...

[DummyLoad]

Very glad to see this work done. The original Silvertone reverb tanks obviously being a weak spot. I wonder if one of those blue plastic tanks I see in pedals would work to fit it inside the original amp head...

Thanks!
I'd go with a tank like in the link below, if that's what I planned to do; metal enclosure construction so better shielding. The issue with the Silvertone cabinets is the location of the PT being located at the center of the chassis, mutual inductance from PT to the reverb tank is an issue, I did test with a type 8 tank and was not satisfied with the hum level. Also, these mods work best with a type F tank, 1475Ω input Z - Those Blue tanks have 800Ω as the highest input Z available and better suited for SS drive/recovery ckts. 


https://www.amplifiedparts.com/products/reverb-tank-mod-mn-8eb2c1b-medium-decay-3-spring-mini

--Pete

[SoundmasterG]

With my brother's 1484 that I modified years ago, I added a Fender circuit and reverb driver circuit to the amp, along with a Fender type reverb tank. I mounted it above the amp chassis on a steel plate, and made a new head box for it that is taller. It works fine one way around, but the other way around it makes noise. I can post pictures later if you like. The original reverb tank was missing when he bought it, so that was my solution. Obviously it sounds great as it is basically a Fender BF setup as far as the reverb is concerned.


Greg

[DummyLoad]

...I can post pictures later if you like...
Greg

Would love to see that work. On that note, I did same when experimenting, if the tank return was closer to the PT, the hum was fairly pronounced, rotated away it was better, but to me, still unacceptable. You resolved that issue with a some added space and fabrication; I'd rather not walk that path, as this amp has the original speaker cabinet, and the head stows in the bottom of speaker cabinet. I suppose that I could modify the cabinet's back panel to accommodate a taller head cabinet, but I'd rather keep as much stock as possible.

--Pete