Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: whalecalls on November 21, 2020, 03:58:11 am
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Howdy y'all,
I just picked up an nearly all original '69 Sound City B100 mkiii for a real good price. I doubt they will, but let's hope the original blackburn Mullards test well. I am waiting for some caps to arrive so I can recap the leaky electrolytics and install a IEC socket, etc.
This amp is similar to a Hiwatt DR103 in many ways, but one main differences is that is does not have a master volume. Once I get the amp up and running safely and assuming its going to be stupidly loud I foresee myself considering installing a MV.
My questions are....
-Has anyone ever installed a PPIMV in a Hiwatt style amp? Normally, Hiwatts a have a MV following the tone stack two gain stages before the PI.
-How do you think a Lar Mar PPIMV would work in this circuit?
-Would there be any tonal benefit of using a PPIMV in this amp instead of placing a MV before the .004 cap after the stack? (A subjective question I know)
-Would there be any dangers or risks installing a PPIMV in this amp? Would it be problematic for the bias stability of the amp?
-Anything else I should consider? Layout, lead dress, component values.
-Also, the cathode bypass caps are 100uf which seem rather insane to me.... Any thoughts?
-Also, if anyone has any experience with these pre-active tone stack Sound City's feel free to let me know if you have any pointers when bringing this amp back to life.
Per usual, thank you all for your input and knowledge. Cheers to a fun winter amp project.
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I think if it were mine I'd do the cap swap and IEC and then use it with an attenuator, rather than drill holes and modify wiring in a near original vintage piece like that. Your amp, your choice, but have a think of the value should you want to re-sell it. Especially if you mod it only to find it doesn't sound great with the MV.
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JB,
I have thought of the resale value and retaining it's originality. I am def going to drill the chassis for a IEC socket and will probably install bias test jacks and such. I plan on using this amp live and for international touring so I am seeking to making it as functional as possible. That being said, I respect and am considering your input.
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The dual bias pot circuit will make the Lamar MV installation a bit tricky. Be careful. I advise against it.
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Sluckey,
Ah, that is a very very good point which I didn't consider. I am glad I ask. Well, if I do go a master it's prob best to insert it before that .004 cap. I think I mainly just wanted to try and install a PPIMV to try one out.
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JB,
I plan on using this amp live and for international touring so I am seeking to making it as functional as possible.
I would suggest burning it in and having a backup plan it the unlikely event of. . . . After all, how well do you know this lady and your going Global with her? You know the girls. They could have a blow out and leave you hanging. . . . I'm all in for a full shake down first.
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Why not simply convert it to Hiwatt spec? That's surely not going to hurt resell value, and you'll have your preamp/master volume right there. I did it to a Mark 4 it sounds like Live in Leeds all day long. But don't expect it to sound like a Marshall. If you want it to sound like a Marshall, check out the 2204 style pre/master volume, I also did this to a Mark 4 :icon_biggrin:
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Silverfox,
I have a feeling her and I will be getting along alright. I am going to bringing this either as my primary touring amp or as a backup at minimum.
Sounctyi85,
It is pretty much a dr103 circuit just without a master and some other small variations. I am going to play it for a while and then tune it to my needs if need be. Maybe I will go with a 2204 preamp down the road.
Thanks for the suggestions y'all! ...... Still waiting on my caps and such to arrive.....