Newcomb h-25 pa to guitar amp

[jtmaupin]

Greetings all,

Attempting my first amp build. Have had this project waiting for me to get to it for some time now. I don't have a schematic for it (if anyone else does and would share, that would be awesome), but it seems straight forward enough. The first question I have (as I am sure there will be more) is on converting the 4 pin mic connectors to 1/4" TS connections. If anyone could shed any light on my project, it would be appreciated.

Here are some pictures

[ATTACH]3767[/ATTACH]
[ATTACH]3768[/ATTACH]
[ATTACH]3769[/ATTACH]

Thanks,

[gldtp99]

I'd remove one of the Channel pots on the front panel and use that space for a 1/4" input.
I'd leave the 4-pin Mic connectors in place and remove the RCA phono jack below them to use as the 1/4" Speaker Out on the back panel---- connected to the speaker Z switch (if the switch is still in usable condition---if not replace it with a new Marshall-type speaker Z switch, it should be a close fit).
I'd also gut that old PA circuit with the ancient pink signal caps and old, drifted, noisy carbon comp resistors. I've rarely found components of this age to be very close to orig values.
I'd build a Tweed Fender circuit with new filter caps, signal caps, and resistors----look at Fender schematics to see if you can use the Octal preamp tubes you have----i'd convert to 12ax7's myself because they're more plentiful, cheaper/easier to find. But that's just me---- i've gotten away from building with non-12ax7 preamp tubes for the most part.
Some don't mind messing with the old octal preamp tubes............gldtp99

[tboy]

I don't have a schematic for it

I don't think I've ever seen a Newcomb amp that didn't have a schematic pasted to the inside of the bottom cover. Is yours missing?

[jtmaupin]

bottom plate

Thanks for the suggestions

as to the schematic:
Some has changed out the bottom plate, now its just a cut out sheet of copper.

[tboy]

I knew I had a couple of Newcombs down in my pile of project-fodder, so I dug them out last night in hopes that one might be an H-25. What I found misses the mark on both sides of what you need; I have an H-15 and an H-50! Hopefully I'll have time over the weekend to remove the bottom covers and photograph the schematics. Maybe one of them will be similar enough to help you along with the H-25.

[tboy]

Newcomb H-15 schematic

Here's a photo of the H-15 schematic:

[jtmaupin]

Thanks for the scematic!

[jtmaupin]

Managed to find a schematic in an old sams book. My question now is, can I use the 9 pin unused sockets that are connected to the mic inputs for 12ax7 tubes. If I can, do I bypass or feed into the 6sf5's. Also should I cascade the preamp tubes like suggested on the tube amp conversion page?

Here is the schematic.

[ATTACH]3834[/ATTACH]

Also I was thinking of removing the remote socket and putting a bypass switch in its place, does this sound like a good idea?

Regards,

Justin

[tboy]

Newcomb H-50 schematic

Here's a photo of the H-50 schematic:

[tboy]

Newcomb H-25 schematic

While moving things around so I could extract the H-15 and H-50 from my basement, I discovered that I actually did have an H-25 as well. It appears to be an older version than yours though, as it has octal sockets for the input transformers where yours has the 9-pin miniature sockets. Here is a photo of the schematic:

[tboy]

Newcomb H-25 gut shot

I thought I should get an under-chassis picture before I begin to mod this thing:

[GreyOwl]

Hi, I'm new to this site and found it by searching for info about the H-15. I am going to be picking up an H-15 in the next week just for getting it out of the pile of stuff the owner has it piled in. I notice a lot of these can be repaired and modified for use as a guitar amp. What I would like to know is, since they have two mike inputs, if more than one of the inputs can be used at the same time? I'm thinking of two electric violins into the inputs then to a decent speaker cabinet. Is this doable or should there only be one instrument at any one time active?

Charles

[tboy]

What I would like to know is, since they have two mike inputs, if more than one of the inputs can be used at the same time? I'm thinking of two electric violins into the inputs then to a decent speaker cabinet. Is this doable or should there only be one instrument at any one time active?

Yes, you can use the inputs simultaneously, but whether or not you really want to do that depends on the kind of sound you're after. If you just want to amplify the violins cleanly, it'll be fine. But if you want to push the amp into distortion to produce an overdriven tone quality, then it would be much better to use separate amps.

[GreyOwl]

Finally picked this amp up last week. It looks to be modified sometime in the past to include three more mike inputs with faders on a panel screwed to the front. There are a few things changed inside also along with what looks to be something shorted in one spot as well as a resistor clipped out of the circuit. Trying to decide whether to redo this to my needs or part it out and build from scratch. Wanting to do what I stated in my first post above and nothing wild just standard amping of two electric violins for my wife.

Charles

I guess I need to double check how to add a picture

[GreyOwl]

Adding Pics