#1
I got this amp from a builder the other day, its circuit is based off a Marshall 1974 I think but currently its unfinished. I was given this amp to test the tone before the builder made some finishing touches based on my feedback and he informed me that there would be some buzz until he finished with the touching up. I posted this as an NAD and it seems there was overwhelming criticism for the wiring. Im not an expert on amps or circuitry and i want to make sure i get my money's worth, What follows is a gut shot of the amplifier and what im asking is, what outstanding issues do you see that i could bring up to my builder and are there any issues you see that appear to be unfix-able?

Some useful details. It runs on 2 EL84's, 2 channel amp. It has 4 12AX7 preamp tubes, and one is either used as a rectifier or a phase inverter, im not sure.







Last edited by ticktockboom at Jul 2, 2011,
#2
can you zoom out a little bit and take a picture and take a picture of the amp from behind as well. the opposite angle of the current picture.

also maybe ask the builder for a picture of what he considers to be a finished amp.
Prs se Holcomb is the answer
Last edited by AcousticMirror at Jul 2, 2011,
#4
Can you get me a picture of the entire amp internals. I'd like to see everything going on in that amp. Especially where the wires from the IEC power inlet are going.

I saw where you asked me about what I meant last night, but I fell asleep before I got a chance to finish with everything and when I clicked post it wasn't there. I'm going to look back over the pictures today and get a feel for what is going on in the amp and then post. It looks like there is a lot of stuff going on that isn't entirely kosher in that amp.

EDIT: And like I said, if you like the amp then its a pretty good deal for a tube amp, the wiring just looks very bad to me. And if the builder is going to be tweaking it to your liking there are a few things he can touch up on.
Last edited by XgamerGt04 at Jul 2, 2011,
#7
so on a scale of 1-10 how unfinished did the builder imply that the amp was?

like was it close to finished and he just wanted to know if you wanted tweaks?
or did he just like want you to hear how it would sound and then he'd work on it for a bit more?
Prs se Holcomb is the answer
#8
Quote by AcousticMirror
so on a scale of 1-10 how unfinished did the builder imply that the amp was?

like was it close to finished and he just wanted to know if you wanted tweaks?
or did he just like want you to hear how it would sound and then he'd work on it for a bit more?


I think he said it was close to finished, but i'm definitely going to bring up the wiring to him and ask him if he plans to make changes. He addressed the issue of the buzzing before he even handed it to me though so there are some issues that i know he plans on fixing.
#9
lemme try and find some other amps in that price range. you said 600?

i'll see if i can find some pictures.
Prs se Holcomb is the answer
#10
Here are my current problems with this amp:

1. The ground wire from the IEC inlet looks to be extremely small. It should be the largest possible gauge wire you can get in that amp. It also looks like it is just soldered to the chassis. This isn't really the best way to go about making this connection and instead it should be soldered to a ring or spade terminal and connected to the chassis between a screw and nut. Ideally the mounting nuts from the IEC jack would be the best thing to use.

2. The heater wiring is extremely poorly done. The wires should be twisted together well, should not jump around the sockets like that, and should generally be kept as far away as possible from the other wires.

3. The use of duct tape everywhere. Pretty terrible if you ask me. Should not be used for this purpose. Duct tape can catch on fire and burn. Should NOT be used in an amp. Nor should electrical tape.

4. The general wiring of the amp is extremely poor. The OT wires go directly across the power amp section. During heavy signal this will have extremely large currents flowing through it and can induce noise in the amp.

5. The Fuse and power switch should be on the same side of the power line, and should both be breaking the live wire.

6. Some of the others have mentioned this, but I myself am not sure. Some of the resistors look to be 1/4W. None of the resistors in this amp should be 1/4W. 1/4W resistors will eventually fail and the amp will be rendered inoperative. If they are 1/4W they should be changed. If they are 1/2W that is better.

7. Screen Grid Resistors. The designer of this amp is showing me they don't understand the intent of UL operation. They have a transformer with UL taps connected to your output tubes. For an amp that will never distort like a guitar amp there is no need for screen grid resistors. In this amp you need them, otherwise you might destroy tubes fast.

I will probably think of more as I look over this... but there are a lot more things wrong with this than I thought. If you like the amp then by all means keep it, but I would get him to fix the fuse issue, add screen grid resistors (1k 5W), fix the fuse/power switch, and redo the heaters.
#11
alright...obviously these amps are done up pretty good which is why I chose these pictures...I wouldn't expect a lot of amps to be wired as well as this at any price point...but they are good for illustrating some things.

first off - transformer wiring is really noisy...ideally you have them at least all rolled up and tucked out of the way.



heater wiring should really be twisted a lot better then he has it.



look how everything is tucked away.



the actual board wiring and everything looks aite.
Prs se Holcomb is the answer
#12
Ok thank you all for your insight and responses, i really do like the sound of the amp and for $600 i dont think i could have done better tone wise. Build quality however is something that i'd like to be at its best, i'll bring these issues up to the builder and see if anything can be done. From what i've read none of the issues are unfixable and shouldn't require a complete overhaul design-wise, correct me if i'm wrong.
#13
Quote by ticktockboom
Ok thank you all for your insight and responses, i really do like the sound of the amp and for $600 i dont think i could have done better tone wise. Build quality however is something that i'd like to be at its best, i'll bring these issues up to the builder and see if anything can be done. From what i've read none of the issues are unfixable and shouldn't require a complete overhaul design-wise, correct me if i'm wrong.


It is all entire possible. Like I said, the few issues I outlined at the end of my post should be remedied. None of which will really change the tone of the amp.