Question about Magnatone - Varistor substitutes [SOLVED]

[kagliostro]

What about the substitution of the varistor with common resistor

and the use of varicap (varactor) instead of usual capacitors ?

or the use of a varicap + an LDR ?

K

[kagliostro]

Whell there is an answer to this question

now thanks to M.P. Manning, the varistors for Magnatone circuits are no longer a problem 

On this tread

http://ampgarage.com/forum/viewtopic.php?t=23839&postdays=0&postorder=asc&start=0

you can find the story and find the solution, this one



Enjoy (and if you can, post a thanksgiving to Mr. Manning  )

K

[terminalgs]

Before you say 'case closed'....


On the yahoo magnatone/valco board, Manning later posted this:


"Well, it looked good on paper, but the sound is clacky with diode switching noise.  Another try is in the works but TBH, I'm not too optimistic."



Ted Kornblum's new Magnatone amplifiers use a circuit with varistors that reproduce the Bonham F.M. vibrato effect. They use current production varistors,  but they don't sell them individually or make it public what specific part# they use or what their source is.. And why would they?  they have a lot of R&D time and effort into recreating the bonham vibrato using current production parts.


Neither did Magna nor Estey/Magna make the part# of the original varistors public.  The schematics just say 'varistor'. Don Bonham originally had 100s of varistors to pick from.  His R&D to get the right ones was very time consuming.  If you look at an old catalog of any of the varistor manufacturers (like globar, Carborundum, Int'l Resistance Co. and GE), you'll see  100's  of unique varistors based on  (1) DC watt power rating, (2) dielectric constant, (3) response time (a percentage of the voltage pulse), (4) operating voltage, (5) peak voltage, and (6) temperature coefficient.


One thing you don't see is the impedances of the varistor (either at low voltage or high voltage), which of course was a critical factor in varistor selection for Bonham to get the desired phase-shift in the bridge.  That impedance didn't act in a vacuum either, the selection of the caps elsewhere in the bridge and their impedances had to be matched.


long story short: Magnatone varistor replacement is difficult. there have been many unsuccessful attempts to find substitutes, and only one successful one (Kornblum's new Magnatones).  Also be wary of NOS varistors on ebay (How do you know they were the varistor model that Magna used, and not one of the other 100 varistors that were produced in the same mold press?)



 

[kagliostro]

I read

Overall, it sounds like the MOV-Resistor substitute is a viable alternative to the NOS varistors, so we can declare a success here

this is at the last post on page 9 of the tread I linked, the author of the post is Mr Martin Manning

and this is the sample to which he refers

https://soundcloud.com/jeremyslemenda/mov-testing

K


p.s.: At the moment I haven't it under hand (and didn't remember where I've seen, because are some years that I'm interesting on this thing) but

the model and spec of the original varistors used by Magnatone are well known and documented

[Zack Engineering]

If this is NOT appropriate let me know, just trying to help the DIY groups.

I have Magnatone NOS Workman Varistors For Sale !!
Genuine Silicon-Carbide, 1/2-Watt Disc with Radial Leads and 1-Watt with Axial Leads
Both have been tested in Magnatone amps and meet or exceed the specifications for DIY Magnatone Pitch-Shifting circuits

Search AMAZON.COM for:  Varistors NOS
Thanks, Zack Engineering
503-757-6654

[zircontweezer]

I tried to search Amazon with " Varistors NOS " but just got a bunch of stuff for nitro fuel supplies.

[Williamblake]

Couldnt find it either. Whatever happened to affiliate links?

[sluckey]

Works perfect for me.

[kagliostro]

When I search on Amazon for Varistors NOS

I obtain a lot of articles like this, like zircontweezer and no varistors

https://www.amazon.com/NOS-14745NOS-Electric-10-pound-Nitrous/dp/B000COXD3K/ref=sr_1_1?dchild=1&keywords=varistors+nos&qid=1612388635&sr=8-1



Franco

[sluckey]

https://www.amazon.com/Variastors-Magnatone-Silicon-carbide-varistor/dp/B08TGV86P3/ref=sr_1_2?dchild=1&keywords=Varistors+NOS&qid=1612391654&sr=8-2

[kagliostro]

Ciao Steve

Thanks, the link you posted works correctly also for me (apart from the fact that varistors are not available)

Franco

[sluckey]

(apart from the fact that varistors are not available)

That link shows them in stock for me. I was able to put them in my shopping cart.

Maybe you need to be logged in to your Amazon account?

[66Strat]

I did a search for NOS workman varistors. Two products from Zack's showed up in my search. Both were indicated to be in stock. I seem to remember Zack having a website 15 or so years ago. Magnatone parts, as best as I can remember, were his niche.

https://www.amazon.com/Variastors-Magnatone-Silicon-carbide-varistor/dp/B08TGV86P3/ref=sr_1_2?dchild=1&keywords=nos+workman+varistors&qid=1612390217&sr=8-2

https://www.amazon.com/Varistor-Magnatone-Silicon-carbide-varistor/dp/B08TGPR8XR/ref=sr_1_1?dchild=1&keywords=nos+workman+varistors&qid=1612390217&sr=8-1

[trobbins]

I may be wrong but Zack may have NOS parts via Gary Croteau (who had I think the largest stock a decade ago).  There are a few Workman parts that appear to work fine (https://www.dalmura.com.au/static/Magnatone%20vibrato%20design.pdf).

The subsequent world of 'Magnatone' and who owned certain rights, and who were trying and did prepare re-issues and clones appears to be historically intriguing over the last 2-3 decades, including some subterfuge along the way by some parties.

Martin's minimalist varistor clone using 22V, 56V and 82V MOV parts is likely the simplest path to take, and it would be great if someone has the time to make some 'swap out' comparisons between NOS parts and such a clone.  I just noticed that smt MOVs at lowish VDC @1mA levels are now quite available (http://www.farnell.com/datasheets/1328356.pdf), so I may try and get some in and build up some clone varistors and do a better bench comparison of the NOS and clone, especially as using a string of say 3 to 10 smt MOVs would be a lot easier than soldering up 36 zeners and locating resistor tap-offs which was my initial try.

[66Strat]

Thinking back, it's probably 25+ years ago. My baby daughter wasn't born yet. She's 25 now. Damn, the candle burns fast when you get closer to the end.   I wonder if there will be NOS tubes on the other side? 

[Willabe]

That link shows them in stock for me. I was able to put them in my shopping cart.

Sluckey, are you going to test them in your Maggi amp or are you thinking of building a Maggi amp or maybe a Maggi preamp with them?

[sluckey]

All I was doing was testing the link since others could not find them. I'm not gonna buy any.

[Willabe]

I thought you bought some when you said you got them in your cart.

I get it now that you were just testing the link.



   

[trobbins]

I should receive a batch soon of 8V, 18V, and 39V MOV's of the leaded 5mm disk type used by Martin, which I'll try and see how well they emulate an OEM part when configured with biasing resistors, as well as get out my Maggie 213 clone and do some spectrum comparisons.

[kagliostro]

@ Steve

Maybe you need to be logged in to your Amazon account?

I've no Amazon account, when I need to place an order I have my son do it, I will tell him to check

Thanks

Franco

[sluckey]

I suspect they are only available in the USA?

[kagliostro]

May Be

Franco

[PRR]

Yes. When I look normally (Amazon knows me and my address) they are in stock. When I change "Deliver to" to Italy, they are not in stock.

[kagliostro]

Thanks PRR

EDIT:

My son verified, also with an account if the shipping is to Italy the product is unavailable

Franco

[dragonworks]

I own two M15s and the vibrato circuits are working in both but I found this thread to be very informative. I have also stocked up on 7189A output tubes.   
Thank you.DW