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    JTM 20 (merged)

    Cool vid --- And I'm sure that Marshall will sell many of them It appears to be different enough from the 4-input/NMV Studio amps they already make to be appealing to many players around the globe I'm not interested in buying one myself however But I hope this will be a successful amp for...
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    Cloning An SV20

    FWIW --- I used a new Edcor XPWR013 PT for my 2nd mini-2204 build: https://edcorusa.com/products/xpwr013-510v-125ma-ct-6-3v-4a-ct?_pos=1&_sid=d4365ac62&_ss=r&variant=41177682051259 It has a rated current capacity of 120mA and gives @360V B+ w/solid state rectifier in my amp --- Just about...
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    Cloning An SV20

    Sounds like you've got a good plan The build itself seems pretty straightforward The turret board construction, simpler FX Loop (Metro, etc) and a PPIMV all seem like good ideas to me ( maybe an attenuator would work better than a PPIMV on a NMV type Marshall --- I don't like the PPIMV I put...
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    SV20h a terrible amp?

    If they are so terrible then why does Marshall sell so many of them ? They can't be that bad I'm not interested in buying a 20 watt NMV amp for $1800 (or less used) But I build my own amps --- Recently I finished two 25 watt Mini-2204 heads with 6L6GC x 2 output tubes One is near-stock and...
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    Just finished my JMP 2204 clone. Totally worth it!

    Good job on your 2204 (re)build When you post pics of any build remember that these pics will be closely examined by many critical eyes They will not hesitate to tell you that "you did this or that Wrong" or "you used XXX parts and you should have use YYY parts" or "your wiring is not tidy...
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    13.5 or ? for cab

    No, 13.5 ohms is ok You are measuring DC Resistance with your multimeter but not the Nominal Impedance of the speaker (which is still 16 ohms) Impedance of a speaker is not the same thing as the resistance (which can be measured directly) Look at this datasheet for a Celestion Vintage 30...
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    Build Journal: Bogen CHB35a to switchable Bass/2204

    These switched pots seem to have the long solid shaft You'd just need to make them into the value(s) you need: Potentiometer - Alpha, Audio, SPST Switch | Antique Electronic Supply (tubesandmore.com)
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    Build Journal: Bogen CHB35a to switchable Bass/2204

    I used to buy Alpha long shaft 24mm pots from AES (tubesandmore.com) that had very long solid 1/4 inch shafts I'd cut the shafts to the length I needed for the CHB series Bogens They don't appear to be available at AES anymore Maybe you could google "long shaft pots" and see if anyone still...
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    Build Journal: Bogen CHB35a to switchable Bass/2204

    Most CHB35A's I used 7868's ---- In some amps I replaced the output tube sockets and used 6L6GC ---- In one I used cathode biased EL34's They all worked well and it didn't make a huge difference what exact type of output tube was used The 7868's might have a slightly earlier breakup but they...
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    Build Journal: Bogen CHB35a to switchable Bass/2204

    Yes, Bogen CHB35A's !!!! I used to buy up old Bogen PA heads and re-purpose them for guitar use and sell them to local bands/players Bogen CHB35A and CHB50 were the most common but I also re-did Knight, Stromberg-Carlson, Bell, and many other brands Bogen CHB35A and CHB50 iron was usually...
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    Pot Values and availability of spares.

    Here's the schematic(s) for that amp: bluesbreaker_reissue__45w_1962.pdf (schematicheaven.net) The two Trem pots are: 1) VR7-- B220k --- a 220k linear pot 2) VR8 -- 1Meg dual pot -- doesn't say if it is Log or Linear but the old pot can be measured to find out for sure---- either one...
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    Hiwatt to Hell

    Interesting project---- I've built many DR504 and DR103 clones for local players (and myself) usually using the Heyboer Partridge clone iron. Which Preamp are you going to use in this one ? I've usually built the Early or Mid 70's 4 Inputs preamps----- I like the big clean tones and prefer to...
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    How rare were purple tolex JMP 2203’s? ( morin Marshall content)

    I don't need to see pics of the OP's purple JMP 2203 I have my own '78 JMP 2203 in factory purple tolex I had to replace the blown original PT with a Metro/Heyboer PT I added a PPIMV in one of the four speaker output jack positions on the back panel I installed new Filter and Bias caps when...
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    2203 Master model JMP 76 weird mods...

    There are many resistors in the amp that could be called "Voltage Resistors". If you're asking about "Bias Splitter Resistors" then 150k is the typical value for 6550 output tubes and 220k is typical for EL34's. Find Marshall schematics for the model you want to restore your amp to and work...
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    2203 Master model JMP 76 weird mods...

    I'd restore that JMP to stock. It probably would sound very good in stock form. I have a '78 JMP 2203 in factory purple tolex that needed some restro work when I first got it. I replaced the Filter Caps and the Bias Caps---- I set up the Bias circuit to run EL34's. Later I installed a PPIMV...
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    Sound City L120 - noise issues

    I don't think an active preamp is a bad idea in itself. But the SC Mk4 active preamp leaves a lot to be desired, IMO---- some people do like them but I'm not one of them. When I did my first couple of SC120/Hiwatt rebuilds I had one stock SC120 on hand that I serviced up and it was a...
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    Sound City L120 - noise issues

    Here's Lalo playing one of my DR504 clones at Trees in Dallas a couple of years ago. He's playing rhythm on this song---- the white head sitting on the Orange cab: He's been using this DR504 clone for more than 12 years touring all over the southern USA, Mexico, and parts of South America...
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    Sound City L120 - noise issues

    Interesting. But there's no reason to mount the transformers in a non-stock position with these amps. The noise problems in the stock L/B 120's have nothing to do with transformer coupling hum. Even though I hear this myth from time to time----- "He turned the transformer 90 degrees and the...
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    Sound City L120 - noise issues

    Here's a SC 120/Hiwatt gut/rebuild I did many years ago played by my friend Harry (doing some blues). I don't remember if this one is an Early or Mid 70's 4 Input preamp circuit----- but it really doesn't matter all that much---- both are excellent sounding. The channels are turned up to give...
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    Sound City L120 - noise issues

    Yes, the Mid 70's 4 Input circuit is a great sounding Classic Hiwatt circuit. I've built that one several times as well as the Early 70's 4 Input circuit. Both are excellent examples of Classic Hiwatt tone. Remember to take into consideration that the Power Supply sections of the Classic...

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