Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Beezerboy on March 11, 2017, 03:26:47 pm
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Hi guys.... noobie here. I've got this 100 watt Carvin head that was $8 at a yard sale. I got it working but the tone stack & eq are rubbish (the tubes test good). the thing has been abused & the maybe used as a door stop to the barn... anyway, its been abused, so what I'm thinking is... parts doner. get the 100w Plexi board and a few bits.... the rest is there. the question is the reverb.... the Carvin has reverb but I believe it is driven by solid state and I don't want to incorporate that. I've built a couple amps & have a fair idea where to insert the signal but would feel better if somebody had a diagram, or could alter a diagram (the 100w Plexi) to be sure. the other question is the power supply on the Carvin..... does it have enough mojo to drive the additional tube that I will have to add?
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What model Carvin is it? For 8 bucks sounds like a fun project
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Welcome.
10 seconds in Google shows perhaps a dozen (probably more) "100 watt Carvin" models over the many decades. Can't guess which have how much "mojo" without a better clue.
I must say I don't think Carvins generally suck. Or can be really "abused". Rat-droppings and horse-chews can be repaired. I think you fix it, it can be a fine amp, even if not your personal "thing". But I suppose with the low demand for Carvins it would not be a sin to rip it apart (in hopes of building something better in the ruins).
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ooop.... sorry. it appears to be the X100B
ya.... I'm told it's a Marshall clone & a pretty good amp. it has a spring reverb tank, but its solid state driven. It's gonna get a makeover.... modify the cabinet & new faceplate too.
thanks for anything you can throw my way
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http://el34world.com/charts/Schematics/files/carvin/Carvin_Schematics.htm (http://el34world.com/charts/Schematics/files/carvin/Carvin_Schematics.htm)
Look under the X-series
The topology and component values don't remotely look Marshall to me. And lots of solid state parts in the signal path as well as the reverb.
It has three 12AX7's and four EL34's. IF you added a fourth 12AX7, you could do a "one tube" reverb.
IF it were mine, I'd gut the amp ............. try to use the trannies and build something I wanted.
With respect, Tubenit
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IF it were mine, I'd gut the amp ............. try to use the trannies and build something I wanted.
+ 1 for Tubenit
Franco
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yep.... I have seen that diagram, and yes, the plan is to use the bits to build something with the 100w Hoffman plexi board.
would like thoughts on 1: how to best insert a tube reverb into the project, 2: will the power supply support the extra tube
I will probably do the Trainwreck master volume and a 3 way neutral feedback switch since I have done those mods on other amps and found them worthwhile. there may be other mods as well
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Unless you are playing HUGE arenas .................. you don't need 100w and you can use two tubes and still have ear shattering volume. IF you lose two tubes, then I can't imagine the PT not being sufficient for one tiny 12AX7. :icon_biggrin:
Here are some options for your consideration that hopefully will allow you to see some ways of a one tube reverb insertion.
Personally, I would do the one I labeled Carvin Conversion ......... IF it were my amp. That doesn't mean you should do that. You should build whatever you want. The Carvin conversion idea uses a mosfet CF which frees up a second triode to be a very effective FX loop and you can still have the one tube reverb with only four 12AX7 type tubes. The CC (Carvin Conversion idea) also allows for a 5879 pentode on the front end, some cool boost features around the tone stack and a PPIMV to keep the volume lower.
Just ideas for you to ponder. :thumbsup: IF you want an editable SCH version of a schematic, just let me know & I'll post it for you.
With respect, Tubenit
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Or just insert a Fender style reverb after the treble wiper.
Deleting two EL34's will free up enough power for ten preamp tubes.
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Good stuff... thanks guys. I like that CC idea... will have to ponder
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Another option would be to take Hoffman's Plexi 50 and parallel V1 and then add an active FX loop and then run either delay and/or reverb pedals
thru the active FX. The active effects loop would also act somewhat as a master volume.
Don't know if you noticed on the Carvin schematic, but the schematic indicates about 455v on the plates of the EL34's. You could use 6L6's if you preferred and don't already have good EL34's on hand?
With respect, Tubenit
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Now that I have actually looked at the Hoffman Plexi50, I have revised the schematic.