DeArmond R15t - Tremolo Help

[O-Fuzz]

Hey All,
First post, and quite honestly totally new to forums in general.

So I'm a VERY, VERY, VERY novice self taught amp 'tinkerer' looking for some help. I've recently acquired a great original DeArmond R15T in lovely condition, but the tremolo doesn't seem to work.

At this point I've re-capped it, and added a 3-prong (photos don't show the new can cap and cord but they have been added).
I've taken readings off all the resistors and all seem well. Nothing 'obvious' is jumping out at me.

I wonder if the problem is that 'varistor' which I know nothing about. I'm also wondering if the problem might be occurring in one of those bright red 'couplets' which I've never seen before in any other amp.

Also, too - might the RATE and DEPTH pots be wired incorrectly?

Lastly I've tried a shorting switch I made (1/4" jack with a couple wires) in lieu of an actual switch - but that didn't jump start the tremolo either.

Any help/questions/info is greatly appreciated...

THX!
O.

[PRR]

Welcome.

> I've tried a shorting switch

Shorted is dead. Shove a pencil, pen, golf-tee in the trem hole to OPEN the switch-jack.   What he said (below).

> those bright red 'couplets' which I've never seen before

They don't get into the trem circuits.

There is a voltage chart. Voltage readings are always a good first step.

[sluckey]

That FS jack needs to ground that 1M to enable the trem.

[sluckey]

Measure voltages for V6 and compare to chart. Post your results.

The voltage on pin 1 will be changing at the rate of the tremolo if the oscillator is working. If pin 6 voltage is steady that means the oscillator is not working either because of a circuit malfunction or the FS jack is not grounding the 1M resistor.

[O-Fuzz]

Hey Sluckey, Hey PRR,

Thank you guys for the replies and suggestions!

Sluckey,
I will take the measurements tonight and post my findings for sure!

Truly appreciate the info and advise.
O.

[pdf64]

Schematic link?

[sluckey]

Schematic link?

Look at the top of the first pic.

[O-Fuzz]

Hey Sluckey and all,

Ok, I've gotten my measurements, and have some interesting albeit maybe disheartening results.

You should know that I brought the amp up on my variac until the filament - pin 9 of V6, was exactly at 6.3vac - this occurred at a wall voltage of exactly 112vac...also note that I had my footswitch plugged in with confirmed ground continuity traced back to that 1M resistor.

And these were the findings:

pin 1 - 155 vdc
pin 2 - 6.1 mvdc
pin 3 - 1.3 vdc
pin 4 - 0
pin 5 - 0
pin 6 - 276 vdc - and STEADY
pin 7 - 155 vdc with NO change when adjusting the 'RATE' pot through its entire range
pin 8 - 158 vdc
pin 9 - 6.3 vac

So as you can see, all my voltages (with exception of pin 9) were low as compared to the voltage chart. But also, no variance of fluctuation of voltage at pins 1 and 6.

So does this mean a definite issue in the actual circuit? Any chance the 'Rate' and 'Depth' pots are shot??

Thanks again,
O.

[sluckey]

OK, first off, I misspoke in my last message. I said pin 6 but I should have said pin 1. Of course, pin 6 will be steady because it's connected to B+. Pin 1 should be fluctuating if the oscillator is working.
 
The Depth pot is not in the oscillator circuit so don't be concerned about it now. The rate pot is not likely bad but you can eliminate it simply by connecting a jumper from the top side of the pot to chassis ground. If the voltage on pin 1 is now fluctuating, then replace the rate pot. The most likely suspects at this point would be a weak tube or those three caps between the plate and the grid. So, replace the tube first and if no improvement, replace the .02, .01, and .01 caps. Any joy?

[O-Fuzz]

Hey Sluckey,

Thanks again for all the useful input!
So yes, of course, pin 6 to B+...I should've known that myself...!
So pin 1 is tied to pin 7...and not fluctuating voltage...

So I jumpered the case of the rate pot to ground...no fluctuating at pin 1...
Then I swapped out a few tubes (a brand new JJ, another vintage Telefunken, and a vintage BugleBoy)...no real significant change to voltages, and still no fluctuation...

now I'm starting to really consider those caps....buuut somehow or another I have no .01's in my parts bins...only .02's...
So I went ahead and put a new .02 in - and still NO fluctuation in pin 1 voltage...

(see pics attached of new .02 installed as well as my shorting switch)

I've gone ahead and ordered some .01 caps, but wondering if - for troubleshooting/testing purposes - can I substitute those .01's for a different value??? I've got plenty of .02's on hand!

Thanks again Sluckey and all!
O.

[sluckey]

So I jumpered the case of the rate pot to ground...no fluctuating at pin 1...

That did nothing because the case is already grounded. Put the ground jumper on the pot lug with the yellow wire and test again.

You can change the two .01µF caps with some .02µF caps. That will slow down the tremolo speed.

You don't need that shorting plug in the FS jack because the jack provides a ground when no plug is inserted.

[O-Fuzz]

Sluckey! You did it!

Slapping those resistors in there got me my tremolo! (see attached, .02's in place of .01's for now...)
I can't thank you enough...

That being said, there is definitely something funny with the 'depth' pot...it doesn't affect the 'oompf' of the effect until after '7' on the dial..in other words...I get nothing from 0 thru 7 on the dial, then 7 thru 10 the effect comes on strong and deep.

The schem calls for 'depth' pot to be  350k - what would happen if I substitute with a 250k?? as 350k pots seem to be quite rare now-a-days...

Thanks again!!
O.

[PRR]

> something funny with the 'depth' pot...

It wants to be "Reverse Audio", what they call "left hand taper". That is important to "feel". However it may never be a smooth even control like a Neve fader.

Me, I would try an alligator clip across the Varistor.

[O-Fuzz]

Thanks PRR,
I'll try the alligator across the Varistor..

So, another question/concern...those red 'couplets'?? How concerned should I be that they would ever fail or more specifically be particularly difficult to deal with should they fail?

The reason I ask, is because I have an opportunity to purchase this amp (as it doesn't belong to me) but I'm reluctant to buy something that may be a headache to maintain should something go wrong with those couplets in the future.

Thanks again all!
OM

[sluckey]

So, another question/concern...those red 'couplets'?? How concerned should I be that they would ever fail or more specifically be particularly difficult to deal with should they fail?

I would not be concerned at all. The schematic clearly shows the circuits inside those PACs. If a component inside one of the PACs failed I would just replace the PAC with individual components. The Inverter PAC would be a pain in the ass but still very doable for a competent tech.

[PRR]

Failure has been very rare. Mid-century hi-fi was full of tone controls and preamp EQ done with these and we don't start by suspecting trouble. There is less stress (assembly and use) at key parts than a discrete build.

But as said: it is the exact same stuff as a hand-wired lug-board except done with ink(*) on jigs. The usual amp and hi-fi modules are documented on a Web. This one is a Custom but the details are on the doc you linked. IF it fails, hotting-up the solder iron is most of the job.

(*)Huh. Yours looks like real resistors; the commodity boards used carbon-ink for cheap ohms.

[O-Fuzz]

Thanks for the input you guys,

Sincerely appreciate the time and attention. Although I still don't quite understand them, you've set my mind at ease about those PAC's...I'll let you guys know if I decide to keep the little DeArmond...as I'm sure you guys already know, these old DeArmonds are extremely rare and quite valuable.

I'm sure I'll be checking in again real soon with my next amp repair. I'm really fortunate to have developed a friendship with a fella that has an amazing collection of incredible old tube amps, and he's asked me to give them all the once over...

THX!
O.