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adding a switchable solid state rectifier to a tube rectified marshall

Discussion in 'Marshall Amps' started by lordraptor1, Sep 2, 2021.

  1. lordraptor1

    lordraptor1 New Member

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    question for the gurus LOL.

    im getting parts together to build a clone tube rectified marshall ( kinda looking in the plexi/jcm800 area of things but tube rectified). so my power and output trannies will be a dynaco ( power) P-782 and a dynaco ( output) A-431 which are actual vintage units out of an old MKII amp :D .

    so, my actual want is to have the amp switchable from tube rectifier to solid state rectifier for more versatility and some different amp characteristics.

    so the question for the gurus, is it possible to take a tube rectified marshall and add a switchable solid state rectifier. i did see the jtm45+ that tube depot had ( i say had because it has been showing back order for MONTHS) however i would rather go 50 watt 2203/2204/jcm800 over jtm45 but will if need be.

    so if anyone has some ideas im all ears ( or rather eyes LOL).
     
  2. El Gringo

    El Gringo Well-Known Member

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    Check out the Fender Prosonic combo as it has a 3 way rectifier switch . Class A -tube, Class AB - tube , Class AB - solid state . I found this to be a versatile feature in tone selection . I liked the Class A -tube as it was like a Vox AC-30 type tone and a really nice and thick tone , and the Class AB solid state . I did not like the Class AB -tube as it sounded kind of thin to my ears . This was a nice combo amp that I used from 1998-2011 when I got the Fender Supersonic amp which was billed as the next step up from the Prosonic . The Prosonic had a great reverb . Also what sold me at the time was the premise of going from clean twangy country (signature Fender sound ) with awesome reverb to distortion city with the special design Celestion 10 inch speakers .This worked very well . So in 2011 I get the then new Fender Supersonic and it has the Fender all tube spring reverb right . Did not work .Repeat did not work . As it had a design defect which the clowns at Fender finally fessed up to me . The Fender jerks at first told me to change and replace the 12AX7 tube that was for the circuit that had the reverb -did not work . What it was doing was making a screeching whistling kind of sound anytime I had the reverb on 2 or above . Now think about this for a second a Fender amp with a non working reverb . I forgot to mention the Supersonic amp came with 2 Celestion Vintage 30 speakers . Also with 2 channels and being able to go from Fender Clean to overdrive for a great lead sound . What a dud and a disappointment because of the reverb issue . Also because they did not fess up to the issue with the design flaw with the reverb .
     
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  3. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    Aren't the Dyna opt's ultralinear? The amp will be cleaner than your usual Marshall I would think...Experts chime in. :D
     
  4. DonP

    DonP Active Member

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    I have 2 ST-70's.

    Yes they are, but you don't have to use the ultralinear taps. The bigger concern is that they aren't "wound" like a Marshall OT, with the same impedance. Might not sound like a Marshall.

    They can handle 35 watts. Going higher will burn them up.

    When switching from tube to SS rectifier, the voltages will go up. Might through the bias off if this is fixed bias.
     
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  5. Kinkless Tetrode

    Kinkless Tetrode Well-Known Member

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    You could just use a plug in SS rectifier when you want to go SS. You will likely need to adjust the bias anyway.
     
  6. mickeydg5

    mickeydg5 Well-Known Member

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    Everything I found says A-431 is rated 60W and the P-782 with a 5U4GB placed 460 VDC on the 6AC7/EL34 plates.
     
  7. lordraptor1

    lordraptor1 New Member

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    this is the same information i found, in fact the dynaco pt and ot came out of a dynaco mkII that i scrapped.

    shows tube compliment of the old kits at 5u4 rectifier and 6ca7/EL34 tubes ( need to clarify my OT is actually an A-431 and NOT an A-430 as shown in the following link). Dynaco Dynakit mkII Power Amplifier Kit Manual | HiFi Engine .

    im looking to build a clone of a tube rectified JTM50/plexi ( or JTM45 in a pinch).

    as far as switchable tube/ss rectifier goes, wouldnt i just do to the build what tube depot did in their JTM45+ kit? from what i can tell they added a switch and 2 diodes and by flipping the switch you either used rect tube solo, or added a couple ss diodes with the rectifier tube for solid state ( basically tube just replaced 2 of the ss diodes) from what i can tell here is the wiring diagram for TD jtm45+ jtm45plus_wiring_diagram_v4.pdf ).

    my pt is actually one of the vintage P-782 with the cloth pushback wires and is 120v only (no 120/240 option). for specs i found it has the following spec: 120 vac, 50/60 hz primary, secondary 410-0-410 @ 200 ma. (1) 55 volt bias tap, (1) 6.3 volt @ 5 amp tap and (1) 5 volt @ 3 amp tap.

    the A-431 i have seen it shown as both 50W and 60W ( depending on what pops up in online search engine).

    i also thought that the 5u4 rectifier tube drew more filament current than a 5ar4 or gz34 so i would be able to use a 5ar4 or gz34 rectifier tube in the build or do i have the filament current thing backwards?. anyway, greatly appreciate the insight, opinions and help. just want to obtain as much info so this build goes off without a hitch because this will be about the only way i will ever get anywhere close to a marshall with the prices on them and the scarcity of something in a combo form ( got screwed by a former employer whom was suppose to get me a JCM800 2x12 combo in exchange for working in his music store but the ^%*&^%^% never got me one and then closed up his shop in a midnight move so i never got my marshall or store credit for the amoount the marshall would have cost me at the time ( employees wouldnt let me use it said i had to deal with him but he was avoiding and still is avoiding everybody as he ripped off a LOT of people). closest i have got to a JCM800 is my old peavey VTM120 and matching peacey cab ( which nails marshall tones quite easily although due to it being a peavey everyone else disagrees until they hear it in a blind test and then they swear it is a marshal ( or if i adjust opposite end of spektrum they think it is a fender twin reverb with the reverb turned off LOL).
     
  8. lordraptor1

    lordraptor1 New Member

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    true but if i had to make the choice i would go for true full tube over the ss rectified tube amps ( basically hybrid )
     
  9. neikeel

    neikeel Well-Known Member

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    You can do this switchable rectifier but your bias voltage will change. The bias voltage comes off one of the HT secondaries and a precise bias current is calculated from the anode voltage on your output plates. When you have SS rectification this will be higher than valve. You may just have to compromise between the two of the voltages are very different.
    The OT you quote is 60w type. Even if lower rated you will not burn it up if correctly matched, just get less output.
     
  10. dro

    dro Well-Known Member

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    My question is....Why?
    I believe its the rectifier that gives the sweet to the JTM45 and the Bluesbreaker.
    That and the greenbacks.
    Why mess with a good thing?
    Jus the opinion of one old asshole.
     
  11. yladrd61

    yladrd61 Well-Known Member

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    I have 2 amps with switchable SS / Tube Rectifiers (1) Fender RI '64 Vibroverb Custom (w Diaz SRV mods) 1 GZ34 and (1) Ceriatone Plexi 101 All Access (2) GZ34's. I prefer the feel and response tube rectifier over the SS on both Amps.
     
  12. lordraptor1

    lordraptor1 New Member

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    because i want to LOL, besides if i were building a JTM 45 clone i wouldnt be asking this question because i could simply follow the tube depot jtm45+ schematic and instructions.
     
  13. lordraptor1

    lordraptor1 New Member

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    ok then can you explain how tube depot accomplished the switchable tube/ss rectification without having to rebias every time the switch was flipped?, what about mesa boogie dual and triple recs and them not needign rebiased every time?

    my whole thought process is really rather simple, i saw tube depots 45+ and saw the rectifier switch and it got me thinking if it was possible to use the technique on other older tube rectified amps.

    outside of mesa i havent seen to many amps with switchable tube/ss rectification however NONE of the ones with switchable rectification required a rebias hence the query of you explaining how amp manufacturers are doing it.

    from what i can tell by tube depots schematic and the other few i have seen a tube rectifier basically takes the place of 2 of the 4 diodes normally found in a ss rectified amp, and that flipping the switch basically just adds 2 solid state diodes into the circuit with the rectifier tube giving what would essentially be the same as 4 diodes ( 2 in rectifier tube and 2 external solid state diodes if that makes sense). however, out of the research i have done up until posting on this forum i have seen never seen or heard anything mentioning rebiasing when you switch from tube to solid state this forum is the first anyone has ever even mentioned it and i could see that if i was removing the tube and using a plug in ss rectifier tube.
     
  14. lordraptor1

    lordraptor1 New Member

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    also i might add i dont like the sound of the greenbacks, persoanlly i prefer the vintage 30's or vintage celestion G12 series ( like vintage 80s G12K-85 speakers.
     
  15. neikeel

    neikeel Well-Known Member

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    Tube depot kind of ‘wing it’. Their PT gives much higher voltages than any JTM45 or JMP50 that Marshall made (490vdc vs 450 for JTM45 and 420-430 for a JMP) and they quite just mA setting ranges for various tubes (6550,EL34 and KT66).
    I think their view is that it is close enough for rock and roll!
    Going by your taste in speakers do you think a JTM45 is the amp for you?
     
  16. Max Gahne

    Max Gahne Well-Known Member

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    @lordraptor1 look at R32 on the tubedepot 45w schematic. It switches in and out of circuit with the rectifier switch and so might be part of how they make that work. I myself haven't looked at it enough to figure it out. When I made my own switchable rectifiers on some of my amps I put a little chain of zener diodes in the SS circuit to match up the voltages. But after awhile I dispensed with the switch setup because once I went SS I never went back.
     
    Last edited: Sep 8, 2021
  17. mickeydg5

    mickeydg5 Well-Known Member

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    You will not have to rebias when switching from tube 5AR4/GZ34 to solid state rectifier. The difference will be between 5-15 VDC most likely and the bias difference of 2mV/mA will not make much of any difference.
     
  18. lordraptor1

    lordraptor1 New Member

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    i think you misunderstood my original reason for post, im not looking to diy from scratch a jtm 45. what im looking to do is make what boils down to a 50 watt superlead or JCM800 2 x 12 combo amp with switchable tube/ss rectifier unfortunatley NO marshalls ever had a switchable rectifier so no schematics for that LOL, and as far as tube rectifier schematics im looking at jtm50 black flag /jmp50 transition.

    i dont really need the switchable rectifier but thought if i could do it why not have the added versatility. with all that having been said, id take the tube rectifier over ss. i think if i could make a tube rectified super lead or 50 watt jcm800 id be all good, although i would prefer a 50 watt superlead with 4 inputs and since it is a build i could drill an extra hole for a master volume.

    however, right now im just looking into the switchable rectifier option, i do know that using plug in one of those ss rectifier tube replacements comes with problems such as instant current surge that tubes dont have as tubes have to warm up, and higher operating voltage in some instances causing overheating issues so im not a real big fan of them also considering tube rect uses the 5v winding from a transformer while ss doesnt as far as i can tell from several sources i have personally talked to.


    ill check the thread later, have to discover the hold up on some parts i ordered for a hammond AO-35 conversion ( bad enough the caps are now costing double or triple in some cases but distributors waiting several days to ship the parts then the carriers dragging their feet or mis directing the parts to the wrong place ( example a fuse i ordered recently went from forida to PR ( PR= Puerto rico), and a capacitor i ordered went from pa to ca then back to pa before actually making it to me in Oklahoma which really irked me to no end but those are stories for another time LOL
     
  19. mountainhick

    mountainhick New Member

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    It is easy to do, but as stated can interfere with biasing.

    How to From Rob Robinette:

    https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Rectifier_Switch

    If your amp is cathode biased or fixed biased with a separate power transformer bias supply wire then this mod will work without any modifications.


    EDIT: you said: "my pt is actually one of the vintage P-782 with the cloth pushback wires and is 120v only (no 120/240 option). for specs i found it has the following spec: 120 vac, 50/60 hz primary, secondary 410-0-410 @ 200 ma. (1) 55 volt bias tap, (1) 6.3 volt @ 5 amp tap and (1) 5 volt @ 3 amp tap.


    You're good to go.
     
    Last edited: Sep 10, 2021
  20. lordraptor1

    lordraptor1 New Member

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    P 782 POWER XFMR - Dynakit Parts mine are grey painted not black like in the linked one but i assume the specs are the same on the black and greay painted P-782 pt's and i havent found any evidence to the contrary.

    my only question regarding what you linked is that i would be using a pair of EL34 output tubes. the schamatic in the robinette link looks like a 6v6 push pull setup. would this make a difference?
     

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