Modding a reverb circuit

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mr_sooty
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Re: Modding a reverb circuit

Post by mr_sooty »

Thanks, yeah they offer an upgrade service to bring the older models up to new specs for a couple of hundred US but you also have to get the amp there and back so trying to find another way.

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Re: Modding a reverb circuit

Post by MikeC »

It seems there have been 3 mods to the MKII - a different MV circuit, different output tubes and a different reverb circuit. Mike Zait (DR. Z) said that by changing the MV circuit he could then get a better, more lush reverb (which he also said was the MKI amp's "archilles heal"). Without a factory schematic I wouldn't want to tinker. You could always try a nice reverb pedal (in the effects loop if yours has a loop)?
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Re: Modding a reverb circuit

Post by RectifiedAmps »

mr_sooty wrote: Thu Nov 26, 2020 8:17 pm Am I right in hearing that you no longer do this kind of work?
Yes, I’m out of the game. Just tying up loose ends then I’ll be focusing on other things (work:life balance mainly).

Your ‘old’ tank is 600 ohms input and the new one is 8 ohms. If the old one was original that’d suggest an opamp driven tank or perhaps transformerless tube drive.

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Re: Modding a reverb circuit

Post by mr_sooty »

No effects loop on mine. It's not really an issue live or I would just get a reverb pedal. It's mainly just when you're plugging straight in at home and just want to play without bothering with the pedal board. I usually end up using my Cub 12 in that situation because the reverb is nicer. And it's just that thing of having a 3k amp and feeling like it's not 'perfect'. But it always sounds great with the band and I still love it otherwise I'd replace it. If I did that I'd feel like I'd be sacrificing otherwise better tone for the sake of reverb. Would be cool to upgrade to the newer version maybe, but you know, money n stuff.

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Re: Modding a reverb circuit

Post by sizzlingbadger »

Agreed, those tanks are not compatible, the new 8ohm tank will not be driven properly by the reverb circuit, probably a very weak reverb will result.
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Re: Modding a reverb circuit

Post by mr_sooty »

sizzlingbadger wrote: Fri Nov 27, 2020 7:48 am Agreed, those tanks are not compatible, the new 8ohm tank will not be driven properly by the reverb circuit, probably a very weak reverb will result.
Yeah only thing there though is that I'm pretty sure the old tank isn't original either. So I need to find out what tank I originally had.

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Re: Modding a reverb circuit

Post by MikeC »

From the Dr. Z forum:- Reverb tank info ( Older: Accutronics 8AB3A1B ), ( Newer: P-RMOD-8AB2A1B ). Both tanks have the SAME model number so are technically the same. The MKI (Older) tank is made by Accutronics, the MKII (Newer) tank is made by MOD. So your "new" tank is the correct model.
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Re: Modding a reverb circuit

Post by RectifiedAmps »

His photo of the ‘old’ tank is stamped 8EB, not 8AB like the newer tank. If the old tank is functional, I’d just put it back in to see if the reverb is better or worse. Otherwise, you’d need to trace out the circuit or find a schematic somewhere.

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Re: Modding a reverb circuit

Post by mr_sooty »

MikeC wrote: Fri Nov 27, 2020 8:29 am From the Dr. Z forum:- Reverb tank info ( Older: Accutronics 8AB3A1B ), ( Newer: P-RMOD-8AB2A1B ). Both tanks have the SAME model number so are technically the same. The MKI (Older) tank is made by Accutronics, the MKII (Newer) tank is made by MOD. So your "new" tank is the correct model.
Oh sweet, I've been trying to get this info from the same forum without much success so thanks for that! I wonder if the one I have in there IS the original one after all then. Possibly I tried a different one and went back to the original, I really can't remember. I know one of them had feedback issues, probably the one from the photo marked 'old' which appears to be entirely unsuitable. Am I reading right that the only difference with those part numbers is that the newer one has the shorter decay? If so that's kinda interesting.

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Re: Modding a reverb circuit

Post by MikeC »

I think you are right :)
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Re: Modding a reverb circuit

Post by RectifiedAmps »

There’s heaps of info here on the Maz 18:
https://ztalk.proboards.com/thread/30034/maz-18-jr

The main thing to note is that only half the 12AT7 is used to drive the reverb (the other half is a wet/dry ‘summing’ stage). But they use a paralleled 12AX7 as a reverb recovery stage. This is the opposite of what Fender does- a paralleled 12AT7 reverb driver and half a 12AX7 for recovery.

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Re: Modding a reverb circuit

Post by mr_sooty »

You can hear the differences between the Reverbs here. Mine pretty much sounds like the Mk 1 on this video. Always thought the Verb sounded a little 'tacked on', like you could still hear too much of the dry signal. To be honest I can't say the verb on the Mk 2 on this demo sounds THAT much better. Little bit though.
https://youtu.be/yTxI8wKk3oE?t=458

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Re: Modding a reverb circuit

Post by mr_sooty »

RectifiedAmps wrote: Fri Nov 27, 2020 10:06 am There’s heaps of info here on the Maz 18:
https://ztalk.proboards.com/thread/30034/maz-18-jr

The main thing to note is that only half the 12AT7 is used to drive the reverb (the other half is a wet/dry ‘summing’ stage). But they use a paralleled 12AX7 as a reverb recovery stage. This is the opposite of what Fender does- a paralleled 12AT7 reverb driver and half a 12AX7 for recovery.
Sweet, should have looked at that thread obviously. Thanks!

I'm thinking I'll just try and accept that my amp doesn't have the worlds best Reverb and one day when I find some money under the couch I'll add something like a Princeton Reverb for washy home jams.

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Re: Modding a reverb circuit

Post by MikeC »

Last thought from me, maybe email Dr.Z & explain that you are way "down under" in NZ and sending he amp to him is impractical. Ask if he'd provide the MKII MV & Reverb changes in a schematic so your local tech can do the mods.
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Re: Modding a reverb circuit

Post by mr_sooty »

MikeC wrote: Fri Nov 27, 2020 11:07 am Last thought from me, maybe email Dr.Z & explain that you are way "down under" in NZ and sending he amp to him is impractical. Ask if he'd provide the MKII MV & Reverb changes in a schematic so your local tech can do the mods.
Yeah I have tried this one without much luck. They seem pretty keen to keep specs to themselves.

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