• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Radio craftsmen c400 monoblocks restore

James Cox

AK Subscriber
Subscriber
20200813_083449.jpg 20200813_083457.jpg 20200813_083513.jpg 20200813_083539.jpg 20200813_083639.jpg 20200813_083440.jpg 20200813_083612.jpg 20200813_083616.jpg 20200813_083631.jpg 20200813_083633.jpg Hey, i recently purchased a lot of old tube amps to refurbish. 3 7591 based receivers (Sansui 1000a, Fisher 500b, and Scott 340b) all 3 seem to have the usual like old leaky caps and missing knob caps but those will be easy to fix. I also got a very rough pair of c400 monoblocks. 1 has been slightly modified with an added volume pot and a new rca jack. However, there has been a pretty good sized hole cut out where the old jack ised to be so the new ome just hangs loose in the hole and looks pretty janky. The second one is stock under the hood but is missing the power cable and tubes. Curriously, neither amp has a power button or switch but i think they were designed that way. Both chasis' are heavily rusted and chrome is pretty pitted.
So, before i go about ordering new parts and rebuilding i want to get the chasis thing figured out. Am i better off getting a new chasis fabricated and chrome plating it myself? Do i loose a significant amount of value by doing that? What if i have a single chasis made for both blocks? Each side would have independent power supplies and i want to keep the same circuit design as orignal. The only things i would change i would be possibly add a power switch for each side and independent volume pots, unless someome has a reason i shouldnt. The other option is to clean the original chasis as best i can and possibly paint it.
What do you guys think? What way should i go on this one? Im pretty new to this, ive only completeted one full restore of a pilot 240 integrated amp and built a bottlehead kit but i plan on recapping the sansui and fisher before starting the c400s, just tryin to get my plan worked out in the meantime.
 
Register to hide this ad
On the RC 400's,The only Right way to do it, is to strip the orig chassis and re-chrome them . Unlike McIntosh that rep Pops are available.
 
Obviously there is a point of no Return, where you invest more on the restoration, than the orig item is worth. I have heard in my system the RC 500's
about 12 Watts per side of Triode sweetness. But the 400's are not the same. Good luck on them I'm sure they will be wonderful sounding.
Bobhorn
 
I see what you mean, the original pla. was to strip the chasis amd rechrome but with the one having a volume pot drilled out and a huge hole cut out where the rca connection is idk if it would be worth it. The other option im considering is having 2 chasis made from scratch amd attaching the front and back plate from the originals to the new ones. Idk i might be in over my head here
 
The other option im considering is getting ahold of Craig ot NOSvalves and seeing what he would charge to do a full rebuild on them. But they may end up being more than i want to spend.
 
Before You decide on rebuilding them I would check to see if the power transformers are Good. the C-500's were known for failing PT's
 
True, the modded one actually works and was on PA duty at some point in its life. The other one im not so sure about. The seller said that the transformer read the same as the working one but i should probably test it myself. If i decide to stick with the orignal chasis is there a way to fill in the holes that were cut out when it the one was modded?
 
Anything is possible if you have a welder or a friend who knows how to do it properly
 
True haha. This is my first time messing with any chasis stuff and i think im going to have to bring these to my tube guy and get his help with the project. First ill handle these recaps on the other amps and get those restored and make these c400s a back burner project. I dont want to rush it and mess it up.
 
The C400s are not extremely valuable these days, and yours less so with the pitted and modified chassis. I think you'd be best off giving up on the resale value side and ordering a pair of stock chassis from Hammond or similar, or if you want to be exotic get custom ones made to the identical dimensions and chromed. You could transfer the name plates. The good news is they should sound excellent and sonically will be well-worth restoring. If you are even moderately comfortable with circuits I would think it would be a fairly easy one to do yourself once the chassis is cut, no need to send it out IMO for a low-parts basic amplifier.
 
Totally Agree Make it Sound Great and Enjoy those C400's. Do they Use 7591's? and will the New not real 7591's Work in them???
BTW Do they run the Tubes in Triode, Like the c500's?
 
See i was thinking the same thing. I feel like i could copy the circut pretty easily and they are super cool little units. If i do a custom chasis do you think it would be better to keep them as monoblocks or put them both on one chasis?
 
See i was thinking the same thing. I feel like i could copy the circut pretty easily and they are super cool little units. If i do a custom chasis do you think it would be better to keep them as monoblocks or put them both on one chasis?
well if it were me id keep them as mono amplifiers on seperate chassis's as they were intended to be.
 
Yeah, the more i think abkutnit i want to try to keep them as stock as possible. Ill most likely add a power switch somewhere. Are there any other safety mods that are recommended?
 
Beyond cleaning of filth and using chrome polish to get the chassis as good as its going to be and some fresh paint on the transformers I wouldn't go nuts about it. Adding a stack of bills into a new chassis or repairs + re-chrome isn't going to improve the sound any. Rivet in some metal plates to bridge the holes, and install the input jack in that plate as needed.
 
Beyond cleaning of filth and using chrome polish to get the chassis as good as its going to be and some fresh paint on the transformers I wouldn't go nuts about it. Adding a stack of bills into a new chassis or repairs + re-chrome isn't going to improve the sound any. Rivet in some metal plates to bridge the holes, and install the input jack in that plate as needed.

Plastic or metal hole plugs in a any number of sizes are available from Amazon or hardware outlets.
 
Back
Top Bottom