Pioneer SR-101

Non-Rickenbacker Guitars & Effects

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Pioneer SR-101

Postby (Tube_Fan) » Sun Feb 25, 2018 12:27 pm

The Pioneer Sr-101 is an all tubed 2 channel spring reverb system with two spring reverb tanks. Each channel has a 6BM8 (pentode-triode) and 12ax7 (twin triode). The 6BM8 pentodes drive the spring reverb tanks through a 5mf capacitor (no matching transformer) which you can see in the schematic. When its turned up, it tends to have a metallic sound which reminds me of the sound inside of the water tank in a water tower. The circuit is designed so that the channel 1 reverb goes to channel 2 and the channel 2 reverb goes to channel 1 (mixes with the direct signals in V3B and V4B). I tried putting in a DPDT switch mounted on the back to switch the reverb to one channel or the other (shown in the pictures attached). Recently, I also put in a treble roll-off type tone control across the reverb level controls between the 12ax7 triodes (dual 500K pots each in series with a 0.0022 mf capacitor). Before I put in the tone control, I used the SR-101 with a Dyna FM3 FM radio and later tried listening to some LP records. To my ears it didn't sound right when listening to some FM radio stations, but sounded better with LPs as long as the reverb wasn't turned up to high. When the reverb is switched so Ch1 reverb -> Ch2 and Ch2 reverb -> Ch1, it produced a nice spacious image effect. Years ago I tried putting together a stereo spring reverb system using two 3 spring Accutronic tanks and a stereo single ended EL84 tube amp that came from a TV repair shop. I built two 12ax7 mixers on the amp one for for each channel for mixing the reverb and direct signals and used a separate stereo preamp to pickup the signals from the tanks. At the time I tried comparing two separate spring tanks with one spring tank shared between the two channels and also tried reversing the reverb between channels. I thought Ch1 reverb -> Ch1 and Ch2 reverb -> Ch2 sounded the best with the FM radio and didn't try records or CDs. The amp had bass and treble controls which I used to equalize the spring reverb signals. These systems could be used with a guitar or other musical instrument.

Some youtube videos on the SR-101

Pioneer SR 101 Valve Reverb Pre Amp demo
https://www.youtube.com/watch?v=hGWWFYKb6Wo

Audrad's Pioneer SR-101 Vacuum Tube Reverberation Amplifier
https://www.youtube.com/watch?v=3POFDyxpyO8

pioneer_sr-101_sch.pdf
(48.6 KiB) Downloaded 14 times
Attachments
SR-101-SW.jpg
SR-101-open.jpg
Last edited by Tube_Fan on Sun Feb 25, 2018 12:46 pm, edited 2 times in total.
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Re: Pioneer SR-101

Postby (Tube_Fan) » Sun Feb 25, 2018 12:33 pm

The tone control and springs can be seen in the attached pictures.
Attachments
SR-101-springs.jpg
SR-101-tone3.jpg
SR-101-tone4.jpg
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Re: Pioneer SR-101

Postby (Tube_Fan) » Thu Mar 08, 2018 8:36 pm

I tried replacing the 0.0022 μf capacitors with 0.0047 μf capacitors in the tone control which seem to work a little better.
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Re: Pioneer SR-101

Postby (Tube_Fan) » Sun Apr 01, 2018 8:53 pm

I heard this effect on TV before.
Accutronics BTDR-2H long decay reverb module for Theremin
https://www.youtube.com/watch?v=2aOym67frc8
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