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 45 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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Re: Pioneer SR-101

Postby (Tube_Fan) » Fri Aug 24, 2018 2:29 pm

I've been working on an old stereo spring reverb project recently. It uses two single ended el84 pentode based amps driven by 12ax7 twin triode tubes and was from an old TV set. Both amps have treble, bass and loudness controls and are used to drive the spring tanks. I found the stereo amp in the back of a TV repair shop and one man who worked there told me to haul everything away that was out back of the shop. I picked up a number of tube based things, too. I added a mixer stage (mixes direct signal and reverb) and a spring tank preamp (on separate smaller box) to the stereo amp and converted it to solid state rectification which reduces the heater load by 1 amp without the 6CA4 rectifier tube in it. I figured by not using the 6CA4 I could power the heaters from two more 12ax7 tubes in the mixer and preamp stages. The plate supply voltage doesn't use much current for the 12ax7 tubes. One reason I put this together again is because it has a low output impedance and I wanted to try it with two Hammond necklace style spring tanks (pictures below) and should work with that. It works good with the more common spring tanks shown on top of the cabinet, but the output is low with the necklace tanks for some reason. It might be that I had the connections reversed. The patent shows the driver is 36 and pickup is 37, which I had reversed because coax was going to 36 and two wires connected to 37 and assumed the pickup connected to the coax because of better shielding. I'm going to put some RCA phono jacks on the necklace tanks and connect them to the modified amp again when I get a chance and see how it works. If the magnets in the tanks became demagnitized I could add small rare earth magents and see how it works.
I got the used cabinet from a music store.
https://patents.google.com/patent/US298 ... oq=2982819
I tried connecting the reverb system to an FM radio and my tubed stereo system and it works well with the straight spring tanks.

Note: I used an ammeter, voltmeter and capacitor checker to check the components and test the amp before and while powering the amp.
Attachments
stereo-amp.JPG
amp-preamp.jpg
amp-cabinet.JPG
Last edited by Tube_Fan on Fri Aug 24, 2018 2:56 pm, edited 5 times in total.
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Re: Pioneer SR-101

Postby (Tube_Fan) » Fri Aug 24, 2018 2:31 pm

The solid state rectifier (9 pin plug, diodes and resistors) and some spring tanks.
Attachments
SSrectifier.JPG
3spring.JPG
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Re: Pioneer SR-101

Postby (Tube_Fan) » Fri Aug 24, 2018 2:41 pm

nekclace reverb tanks
These tanks have a longer delay time compared to the smaller straight tanks (in pans).
Attachments
necklace.JPG
necklace3.JPG
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