1971 Super Six Reverb

[BrownIsound]

Picked one of these behemoths up a couple weeks ago. Previous owner had said they used it as recently as last summer, so I did fire it up just to see how she sounded, and she sounded really nice, no noticeable hum or bad noises. Pots are very dirty when using them. Tremolo also doesn’t work.

All Chinese tubes, and based on the same branding across all the similar types (of which I am unfamiliar), I would venture to guess at some point the amp had a bad tube, and the owner was convinced to change them all, and whoever did pilfered all the good original tubes.

But anyway, after opening it up…whoa, an almost untouched amp, save the v8 screen resistor. Even the original filtercaps, with the first 20uf having dry capacitor barf on one end.

So, while awaiting new filtercaps to be delivered, I have begun to measure all the resistors. Surprisingly so far, all them appear to be in spec, the worst one near the edge of spec being the 220k mixer from the trem channel reads about 185k. Haven’t finished going through the whole amp yet though. Also noticed a deviation from spec in the resistor off the bias tap from the
PT is 1k instead of 470ohm on the schematic, and the auxiliary power outlet has the hot and neutral reversed.

So I plan on replacing the PS filtercaps as well as the bias circuit filter caps, and trying to fix the trem (could be the tube, didn’t swap while I had it on). But since it sounded so good, I am hesitant to change anything else out that doesn’t need to be changed.

When I get the filtercaps replaced, I’ll fire it up and check for leaky coupling caps. Outside any other problems I find, am I asking for some near term future problem by not changing anything else out? Diodes?

[bepone]

0.1uF from PI to the output tubes change for the new ones , just to save the tubes in case of possible leak ..715 orange drops series

[sluckey]

Tremolo also doesn’t work.

You need the footswitch to enable the tremolo. Or, you can just ground the tip of the vibrato FS jack to enable.

[BrownIsound]

Tremolo also doesn’t work.

You need the footswitch to enable the tremolo. Or, you can just ground the tip of the vibrato FS jack to enable.

I do have the Footswitch. Clicked the button a few times, but no tremolo. I “thought” I heard a very faint ticking during trying the switch.

[xtian]

Stronger filter caps may cure the tremolo, and a stronger tube also may help. I'd replace the white Mallory cathode bypass caps as well.

[Stevem]

As posted, short the trem jack to confirm if there’s a issue with the tremolo.
If the shield in the reverb foot switch is bad then you do not have the needed ground path to activate the tremolo.

A easy and nice power supply up grade is to replace the power supply diodes with fast recovery types, or at least install .001 uf 1000 volt ciramic caps across each original diode.

Just all of those CTS brand Alnico mag speakers are worth some good bucks by the way!

[BrownIsound]

Just all of those CTS brand Alnico mag speakers are worth some good bucks by the way!

Yeah, that originally caught my eye as a fallback if things were found to be bad with it, but so far so good. All 6 have the same date codes (40th week of 71). Someone with a silverface super reverb would want to have these…but sorry, they will be staying in the superior Super Six Reverb, thank you very much.


Almost ready to fire it up without tubes and make sure the PS is working correctly.

[Smitty]

I like soul controls on big Fenders. 10K pot wired as a rheostat in the extension speaker jack to vary the amount of negative feedback. Or you could change the 820R feedback resistor to 1.5K. Really opens up the amp.

I just reformed some old Mallory power supply caps and at rated voltage all had less than 25uA of leakage. I put them back into on otherwise stock 1970 Twin Reverb. Just changed the bias balance to bias level and the soul control. Brown drops. No blackfacing. Sounds great.

I have a near-museum-quality Super Six Reverb that I really like. Transition into overdrive is very smooth. Won't be gigging with it any time soon.

[BrownIsound]

Fired it up with the new PS and BS caps, and adjustable bias. Sounds great, very low noise, but still no trem. I dont see any light being emitted by the roach, but didn’t get further. Next I’ll manually short the jack connection, check the v5 voltages, and swap the tube if it still doesn’t work. Did not hear any ticking this time, that might have been a figment of my imagination the first time I tried the amp?

[BrownIsound]

Well, the roach does light up when shorting the Jack directly.

But the vibro shunting affect is weak.

Here’s the v-5 voltages:
(Vibro “off”)
1: 429V
2: -36V
3: 0v
6: 380V
7:-36V
8: 5.8mV

Vibro “on”, intensity and speed at “1” (shorting jack input to ground, roach pulsating ~2.5x/second):
1: 130-390V
2: -2.3-+1.4V
3: 1.6-2.6V
6: 320-380V
7: -14-+12V
8: 18-21V


So maybe a component out of spec, or the LDR itself is not good, or the bulb isn’t lighting with enough intensity?

[BrownIsound]

Roach LDR reads 20ohms at 1 intensity, and between 37-43K at intensity =10. I’m sure my multimeter is limited in reading the oscillating values, it’s a cheapie Radio shack one.

[Smitty]

The LDR half of the vibrato roach needs to be in darkness to work properly (high resistance in off mode). The only light it should see is from the neon bulb. Sometimes I put the chassis back in the cabinet and the vibrato is much stronger. If the average signal gets weaker as you turn up the intensity then this may be your problem. With the amp off, what is the resistance across just the LDR if you disconnect it from the intensity pot? Try covering it up so no light gets in. Should be pretty high with no light on it. A couple megs. If it isn't then your roach is bad.

[BrownIsound]

In the dark didn’t change anything, nor did swapping in a different good 12ax7 into v5. With the roach disconnected from the pot, it read about 3M. With the light flashing, the lowest reading I got on the meter was 280K.

Again hard to say with oscillating readings, but I would think that lighted resistance needs to be much lower to get a good trem effect, the pot is 50K, so it would need to be much lower than that I would assume.

[BrownIsound]

Ordered a roach from Antique.

Besides possibly playing with the NFB values from the speaker, is there anything to be had by altering the other feedback circuit (220k/.01uf from the PI output)?

[BrownIsound]

Removed out the old roach and instead the new one. Tremolo works good now.