Advice on replacement reverb tank for Peavey XR-500 Mixer Amp

[lassoharp]

This mixer used a tank with input Z of 100 ohm  and output Z of about 300-500 ohms.  Peavey doesn't stock them anymore and all the current production tanks use 2250 output Z.  (Accutronics will make one with 500 ohm output Z but nobody has them).  My question is will it even matter?    Or do I need to be concerned with getting a lower output Z tank? 

 

[analogguru]

The correct input impedance is more important because the driver is working in current mode.

The output is loaded with 100k so it doesn´t matter if it is 500 Ohm or 2250 Ohm.

 

[lassoharp]

That makes sense.  Thanks!

 

[JohnRoberts]

This mixer used a tank with input Z of 100 ohm  and output Z of about 300-500 ohms.  Peavey doesn't stock them anymore and all the current production tanks use 2250 output Z.  (Accutronics will make one with 500 ohm output Z but nobody has them).  My question is will it even matter?    Or do I need to be concerned with getting a lower output Z tank?

I used to be the manager over the engineering group that designed those. The bad news is I have no specific recollection about the pan used in the XR500, in fact over the years there may have been more than one. The only good news is I know a little about the engineering involved.

Back in the day Peavey literally used truckloads of reverb pans and we had a bunch of different ones in the system. Guitar pans were voiced different than mixer pans and there were even different versions for different mounting orientations. While not obvious but in use the spring will sag down due to gravity, the driver and pick up mechanicals are engineered with a specific orientation in mind. If you use a vertical pan mounted horizontally or vice versa the spring may mechanically bottom out too easily from external vibration and handling.

If you know what year your XR-500 was made you can probably get a copy of the schematic.

I don't expect the drive circuitry to be a true current source, but probably a healthy output voltage source through a series resistor (these are not high end products). 

When you say current production tank, which/who's current production?  Peavey may still put tanks in cheap guitar amps (maybe?) but I'd bet money they don't put tanks in mixers anymore.  Cheap digital efx are probably cheaper than even the cheapest spring reverb.

A guitar tank will be voiced differently than a powered mixer tank... Don't ask me to give all the details because I don't remember them, just that they were different.

Do you have the old tank?  What's wrong with it? It may just be a broken wire or solder connection in the send or pickup transducer. I am pretty sure the springs don't wear out. You best bet for stock sounding repair, is to fix the old tank if possible... Not rocket science, but science.

If you decide to go with a replacement tank and it has higher output Z that just means more windings on the output transducer so more output voltage.  Again looking at the schematic might suggest the best way to scrub off some extra gain, I wouldn't pad it down, to then boost it back up again, reverbs never were very quiet to start with.  Too much tank output could distort the fixed gain preamp.

Note: I higher Z pickup might (?) also pick up more transformer hum. It was always a balancing act to mount the spring inside a powered head without too much hum. I would expect this to be linear, so scrubbing off gain in the preamp should get S/N  back in line. In fact the hotter pickups should deliver better S/N

JR 

PS: When we started making guitar amps over in China we literally had to ship US made reverb tanks to China, since they were never able to source a Chinese made spring reverb that didn't suck... 

 

[lassoharp]

I used to be the manager over the engineering group that designed those.

Can't beat that.  They're rock solid.  I've had at least 4 of them in my hands over the years and wish I'd kept them.  People laughed at them as PA heads but they're superb keyboard amps.  I'm really curious if they used the same circuit for the KB 300 series.  The EQs may be a little different but the output power and the compression sound the same.  The XR 500 is even more versatile as a keyboard amp because you have 5 channels with 2 inputs per so you could run up to 10 different keyboards vs the 3 on the KB-300.  I like the sound of the compressor for guitar a lot.  You can get that BB King tone all day long.

If you know what year your XR-500 was made you can probably get a copy of the schematic.

Any idea how to date?  code stamp?

When you say current production tank, which/who's current production?  Peavey may still put tanks in cheap guitar amps (maybe?) but I'd bet money they don't put tanks in mixers anymore.  Cheap digital efx are probably cheaper than even the cheapest spring reverb.

Accutronics and MOD are the two most common.  There's also Belton.  They make a wide range of sizes and I did manage to find one with a very close input Z match.  The tech at Peavey said the old tank had been discontinued for at least 7 years or so.  He couldn't find any specs in the computer system for it.

Do you have the old tank?  What's wrong with it?

Yes, it's an OC Electronics type 247. Short spring.  Output coil is reading open.  There were a couple of different forum posts on web where somebody had same problem.  The coil looks to be snap in.

If you decide to go with a replacement tank and it has higher output Z that just means more windings on the output transducer so more output voltage.  Again looking at the schematic might suggest the best way to scrub off some extra gain, I wouldn't pad it down, to then boost it back up again, reverbs never were very quiet to start with.  Too much tank output could distort the fixed gain preamp.

I can probably get the schematic from Peavey.  Closest I could find on web was for the XR-600 which used a long spring tank and had Lo Z mic inputs but seems to be basically the same mixer amp. (attached)

The higher output could be a problem if it clips the return too early.  I know the reverb on my KB-300 was always on the weak side compared to your typical guitar amp so maybe it won't be an issue.  I seem to recall the XR-500s I had in the past having that same lower output reverb to them too.

A guitar tank will be voiced differently than a powered mixer tank..

The old tank used a 2000pf  across the output. 

 

[JohnRoberts]

I used to be the manager over the engineering group that designed those.

Can't beat that.  They're rock solid.  I've had at least 4 of them in my hands over the years and wish I'd kept them.  People laughed at them as PA heads but they're superb keyboard amps.  I'm really curious if they used the same circuit for the KB 300 series.

Probably close but not exactly, the keyboard amps IIRC were very similar to bass amps but a little wider/flatter frequency response (sealed/ported? cabinet).  More hifi than an instrument amp. KB300 ,just guessing from the name is probably the same power amp module as was used in XR600 (300W?)

The Schematic you posted for an XR600C is actually before my time, I was involved in the XR600E and XR600F re-release cycles.  In fact I recall doing an XR560D (?). IIRC it obsoleted the XR500 and used a digital EFX instead of spring reverb (the digital EFX instead of spring actually made the design effort simpler, and simpler was good for this engineering manager  8) ) .

Prior to my Mixer Engineering group being formed, all of these products were under Analog Engineering (Jack Sondermeyer RIP). I had no reason to fix power amp modules that weren't broken. I used to only half joke that Jack had forgotten more about amp design than I would ever know. He designed amps that could take a lickin and keep tickin, and sounded pretty good in the process.

The EQs may be a little different but the output power and the compression sound the same.  The XR 500 is even more versatile as a keyboard amp because you have 5 channels with 2 inputs per so you could run up to 10 different keyboards vs the 3 on the KB-300.  I like the sound of the compressor for guitar a lot.  You can get that BB King tone all day long.

If you're talking about the DDT (clip limiting) probably exactly the same. It was a pretty benign sounding fast-attack, fast-release peak limiter.  Used in pretty much "every" amp channel Peavey made.

If you know what year your XR-500 was made you can probably get a copy of the schematic.

Any idea how to date?  code stamp?

Count the tree rings in the wood...  ;D ;D Kidding. I am not that familiar with XR500, The XR600 was the big dog, several thousand a month top ten product. If I obsoleted the XR500 badge in the mid 1980s surely older than that. 

When you say current production tank, which/who's current production?  Peavey may still put tanks in cheap guitar amps (maybe?) but I'd bet money they don't put tanks in mixers anymore.  Cheap digital efx are probably cheaper than even the cheapest spring reverb.

Accutronics and MOD are the two most common.  There's also Belton.  They make a wide range of sizes and I did manage to find one with a very close input Z match.  The tech at Peavey said the old tank had been discontinued for at least 7 years or so.  He couldn't find any specs in the computer system for it.

OC might have been in the spec file as a second source but probably accutronics, or an OC version of an accutronics tank.

Do you have the old tank?  What's wrong with it?

Yes, it's an OC Electronics type 247. Short spring.  Output coil is reading open.  There were a couple of different forum posts on web where somebody had same problem.  The coil looks to be snap in.

winner winner chicken dinner...  If you can source a replacement pickup or steal one from another reverb you will be back in business and sound the same.

If you decide to go with a replacement tank and it has higher output Z that just means more windings on the output transducer so more output voltage.  Again looking at the schematic might suggest the best way to scrub off some extra gain, I wouldn't pad it down, to then boost it back up again, reverbs never were very quiet to start with.  Too much tank output could distort the fixed gain preamp.

I can probably get the schematic from Peavey.  Closest I could find on web was for the XR-600 which used a long spring tank and had Lo Z mic inputs but seems to be basically the same mixer amp. (attached)

The higher output could be a problem if it clips the return too early.  I know the reverb on my KB-300 was always on the weak side compared to your typical guitar amp so maybe it won't be an issue.  I seem to recall the XR-500s I had in the past having that same lower output reverb to them too.

I seem to recall from the engineering involved that too much gain on the return caused noise floor issues, etc. Even run-away from power amp talking into the pickups... always several things going on inside the box.  You don't want to re-engineer the entire tank system for just a simple repair (trust me).

A guitar tank will be voiced differently than a powered mixer tank..

The old tank used a 2000pf  across the output.

?? Who knows, perhaps to cut down on HF crosstalk for stability... perhaps the spring was too bright for vocals?  I seem to recall stories about amps talking into reverbs at max gain and causing ultra sonic oscillation

Sorry I have no specific recollections about XR500 lots of generalities I guess it was before my time.

JR

 

[PRR]

Use the 2250 coil. Output level will roughly double. If you have a near-fit schematic it should not be hard to half the gain somehow. Schem you posted, change R111 to 3.3K.

FWIW, the driver *does* appear to be Current Drive, tho with a mere '4558 it isn't cooking the coil.

 

[lassoharp]

Schem you posted, change R111 to 3.3K.

Thanks PRR!

 

[CJ]

here is another pan vendor>

http://amprepairparts.com/reverb.htm

where do you get the Z specs?  not the same as DCR,

tried a 2.5k/2.5K in a Fender amp that wants a 8 Ohm/2.5K and is worked great, so an exact match is not critical, as long as the mis-match is in the right direction, loading a 2.5K with 8 ohms would probably be bad,

also note that there are different configurations as to grounding the I/O jacks on the pan, some float one of the jacks, some have both grounded, could cause hum if you do not observe this,

bought a MOD tank for a Princeton as was surprised by the quality,  Revisit is about 10 bucks more, but maybe worth it, there are A/B tests on youtube for some tanks,

have rewound coils on reverb pans, not any more, real pain soldering the wires with the tiny magnets on them, and when you take the core apart, trauma takes place on the hi nickel lams, best way is to get a junk tank and drill out the rivet and use the whole coil/core assy, good idea to bypass the molex connector, or even wire the RCA cable directly to the coil leads for max signal transfer, you want to squeeze out all the juice you can as the output level is close to the noise floor, (10 mv or close)

Gerald Weber recommends soldering the middle spring  junctions if there are any, maybe not in a short pan, and stuffing toothpicks between the coil and core to prevent mechanical neg feedback, (holds coil tight to core)

Peavey is #1 for tech support, fast and friendly, might also have some back revs on your amp,

here is a parts source  for Peavey stuff, weird spider pots included, ;D

http://www.amprepairparts.com/peavey.htm

user manual>
http://assets.peavey.com/literature/manuals/80322001.pdf

service manual here-download link under schemo preview, don't click on the sucker link for pdf to doc software!
http://elektrotanya.com/peavey_xr-500c_mixer.pdf/download.html

here is a 247 on evilbay  $9.99, could be used or scrapped for parts,

http://www.ebay.com/itm/OC-Electronics-CASCADE-REVERBERATION-DEVICE-Vintage-All-Original-/181825956970?hash=item2a55abec6a

 

[CJ]

pics<

 

[analogguru]

It is fascinating how many "experts" are discussing in this thread.

.... This mixer used a tank with input Z of 100 ohm  and output Z of about 300-500 ohms. .....

This is obviously technical BS.  "Z" is the impedance, from where do you know the value ?  On the label is nothing printed.
Looking at this (finished) auction:
http://www.ebay.com/itm/O-C-Electronics-Vintage-Cascade-Spring-Reverb-Tank-Type-247-Made-in-the-USA-/131440186053?nma=true&si=ELNR2t7uTdPR0fik5QHwo1ABl4c%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

the seller writes:

This is a USA made Vintage O.C. Electronics Cascade Reverb, Small Tank, Type # 247. This came out of a Peavey XR-500 PA head. Ohm test on input 94 Ohms and output 367 Ohms.

"Ohm test" means the DC-resistance and NOT the (AC)-impedance.  The (AC)-impedance - "Z" - will be much higher.  I would say input impedance approx. 600 Ohm and output impedance in the range between 2k and 10k.
So all "expert speculations" on overloading are simply BS. 

Question for the "experts":
The maximum gain of the recovery stage is 66 (100k/1k5) - or approx. 36db. The recovery amp (TL074) is running on +/- 15V.  How much signal is needed to overload the recovery amp ?  Which reverb spring delivers this signal ?

.... The old tank used a 2000pf  across the output.  .....

Then it was modded.  Originally there is only a 100pF capacitor in parallel to the load resistor (100k).

If you know what year your XR-500 was made you can probably get a copy of the schematic.

The XR-500 was made approx in 1980, and if it is a XR-500C then it was made approx in 1986.

Summarizing the above you can replace the spring with a Belton BS2EB2C1B or if you don´t want to follow my (initial) advice then do a search on ebay for an original one.

Used, but working units sell between $ 1,--:
http://www.ebay.com/itm/O-C-Electronics-Vintage-Cascade-Spring-Reverb-Tank-Type-247-Made-in-the-USA-/131440186053?nma=true&si=ELNR2t7uTdPR0fik5QHwo1ABl4c%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

and $ 12,99 :
http://www.ebay.com/itm/Vintage-OC-Electronics-Cascade-247-Reverberation-Reverb-Tank-/151566534395?nma=true&si=ELNR2t7uTdPR0fik5QHwo1ABl4c%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

EOD

 

[lassoharp]

where do you get the Z specs?  not the same as DCR,

I measured the input on the one I have - first DCR then AC  Z with a a meter that measures AC Z (looked at 1K) and got 100 ohm DCR and 138 ohms AC Z.  So I guessed 150 ohm as the nearest standard size based on that.

For the output Z I used the figure off the ebay auction that analog guru pulled up.  That seller measured 367 ohms DCR so came out roughly to 500 ohms if I followed the same ratio the DCR to AC meter gave me on the input.

I am curious about the 10 X rule for coils.  That would suggest about 3Kish for the output and 1Kish for the input.  Those are under the radar for what Accutronics offers.  And so are the other numbers I was guessing (150 In  500 Out)

http://www.accutronicsreverb.com/

What do you think CJ?    The meter I have usually  gives a number that reflects the higher Z even if its off a little.    Loading of the spring causing the lower number?

bought a MOD tank for a Princeton as was surprised by the quality,  Revisit is about 10 bucks more, but maybe worth it, there are A/B tests on youtube for some tanks,

MOD is on its way already.  Havent seen the Revisits yet - need to check those out

Peavey is #1 for tech support, fast and friendly, might also have some back revs on your amp,

Amen.  Wish more companies followed their model.  They tend to keep every part for everything they've ever made on hand.  Didn't have those old OC tanks though

here is a parts source  for Peavey stuff, weird spider pots included, ;D

http://www.amprepairparts.com/peavey.htm

8)  Right on time with that link!  There was busted pot in this one and needed to find one.  Thanks!

"Ohm test" means the DC-resistance and NOT the (AC)-impedance.  The (AC)-impedance - "Z" - will be much higher.  I would say input impedance approx. 600 Ohm and output impedance in the range between 2k and 10k.
So all "expert speculations" on overloading are simply BS. 

I just explained how I arrived at those numbers above.  Seems like it could be either and yes, using the 10 X rule makes sense.  I strayed from that because of what my meter read, and the closeness of values on the Accutronics pans. 


http://www.accutronicsreverb.com/

 

[JohnRoberts]

The driver *does* appear to be Current Drive, tho with a mere '4558 it isn't cooking the coil.

Yup at least that XR600c was roughly current drive.

I stand corrected (again). 

JR