One thing I notice now after looking at a few Hiwatt schematics,
is that there does seem to be an attempt to follow the older Hiwatt scheme of things,
at least here and there.
I think Tube 1 is a variation of the normal channel on the Hiwatt sa412.
On the old Hiwatt the other half of the tube  would be the brilliant channel.
We see similar values, the big 1m resistor at the beginning and so on.
Not exactly the same thing, but there is some resemblance.
The new Fernandes amps are a little different.

I think it's a bit of a mish mash of different Hiwatt amps, not an exact duplicate of anyone in particular.
Perhaps the Sterling Import one, but there are a lot of hiwatt amps without much info on them.

It took a bit of time, but with good photos all is possible.
Anything I wasn't sure of I put a question mark.
I'm not sure how to do a proper schematic from the board though.

I sent it to my tech as well so maybe he can figure something out as well.

I really would like to solve the problem, because this amp does sound quite good!

This amp might be an improved version of a Hiwatt made by Sterling Import in California,
in the eighties.It had the exact same name and controls and a 10 inch speaker  and a similar more Marshall type sound rather than classic Hiwatt. Of course it had a hum and buzz problem too but not on all of them. I can't find any pictures of that amp though.
At least on the Korean version they separated the tubes from the main board.
The american one had plenty of tube problems because the tubes were on the board.

How are the tubes usually connected to the board?

I drew out the board!
This is the view from the component side.
I would say this is 98% accurate.
Just one or two numbers I couldn't see clearly.
Would this help my tech at all?

There is a piece or gap at the top of the board is that by design?

Let me know if anybody spots a problem with the design.
I revised the image with the correct jumper wire position at the input.
I revised R22 which read r27 on rev.1 next to tube 4

You never know what's going to happen in life,
even to people who are very experienced. Tragic things happen,
so you never know.
I'll let you know what happens with amp,
I have a good feeling about it.

Yes it's a rookie mistake
I figured it out after the first one!
But I removed the pigtail monster that was on R5
with a single 1.5 k resistor. They left quite a bit of flux I think on the board there.
Also R22 was the wrong value: 100k instead of 220k,
so that was fixed.


I sense a slight improvement in that I can use the gain at any setting with the Master very very low. Before there seemed to be a buzz even then.
Is this a gain controlled preamp?
I think it has more in common with the DR504 this amp.

I have found a very experienced and very good tech and we are going to see what we can do to improve things.It's a free estimate so I'll let you know what happens.
I'm too chicken to mess with the high voltages.

Bad resistors ?

The piggy back resistors are ok. They are 2  x 3000 or whatever the right value is.
Should be replaced with one 1.5 1/2 watt.

Here's what i found so far:
board values are first my readings next:
R6 470k  298
R7 330k  245
R8 470k  298
R20 220k 185
R22 Wrong value! 220k on board, 100k

I would say there is a strong probability that the caps are bad too.

I will list all the values later .
I am getting odd readings on the preamp pots.
With the controls full blast, for mid I get 46 instead of 100.

Gain is 455 for 500k so ok.
Mater Volume is 211 for 250 so ok.
Are those pots bad or does it have to do with the circuit?

I tried to check the sockets but I must be doing that wrong, because from pin 9 to the ground on the chassis I get zippo.

The blue wire is for the standby switch.
The standby switch is not grounded to the bolt.
The green wire is from the transformer.

Would more photos help?
They told me the values on the board were returned to stock.
Would changing values to match more the real Hiwatt help?

Hi,
Didn't mean to get into an argument!
I meant that Hiwatt used 4 tubes in the preamp in a lot of their amps.
Of course I need help. A lot of it.

I am just repeating what was told to me by these repair people.
It's Class a and a quality amp so they said.
It's debatable. Does sound good though. Actually quite good indeed.
The tubes were replaced by them but one I think has quickly started to squeal when I turn it up.
It's uncertain that the caps and so on were checked .
I couldn't get a straight answer. Yes one day no the next.
They saw a problem, what can I say?
The static is a problem for sure. No doubt about that.
Could bad solder joints cause that?
I'm uncertain how to check
the pins on the socket. Which ones are 4 and 5 and so on.
Can you circle them?
The amp has been off for about 24 hours now.

Take a look at some other hiwatt amps. The 4 tube preamp design is classic hiwatt.
This is not regular hum! Hiwatt amps do not distort like crazy.
It's not some kind of super high gain sounding amp.
None of the hiwatts aside from the hiwatt hi-gain series are.
The problem is not with opening up the master all the way. You have to understand that.
There seems to be extra hum from somewhere. The possibility mentioned was the power supply section. Sure it could be like you say. It has to be checked out. The buzz is definitely a problem.

Hi,
It's not a high gain amp though.
At low levels everything is fine.
There seems to be a buzz coming from the gain control.
The thing is it was diagnosed as 60 hz hum and static. That's not normal.
The amp sounds quite good in actual fact. Very much a Hiwatt vibe.
Great clean sound and nice distortion, not high gain.
I think the mod was to get rid of the buzz.
The real Custom 20 has the exact same valve configuration.
I spotted that cut wire too and they didn't fix it despite my pointing it out.
I'm not opposed to modification, but we have to rule out some of the ideas mentioned.

That's a beautiful amp.
Looking at it I can only I think I can wire a copy!
Famous last words.
But yes I will get the amp back,and figure out what to do.
I will post more pics.
If it's not the filaments or perhaps a dried out cap, what could it be?

Just spoke to my guy.
He's worried that if we go ahead and repair it because there may be a design flaw and it will still hum. He can't guarantee it will work.He wants to know if it's a known issue with the amp.
He told me if there was a problem with the filament wires the tubes wouldn't light up.
If I want to check the caps and diodes possibly the filament wires they will charge another 60.00. He doesn't seem to think it's a component problem.
Could the ceriatone board fit in here? Their layout is free.
The thing is I would try to keep it at 20 watts.

Yes, that's me everywhere trying to get help.
Maybe you should talk to my repair place, but I think I'm just going to get it back
and just get rid of it.I'm going to phone them today.

This is a one channel amp as well.
It drives me nuts that you can fix it while all I get here is:
it's a piece of crap and can't be fixed!

Would more photos help?
You can always try to explain what to do anyway.

Link to photo of components before repair.
Also They seem to think the problem is in the power supply section.
Without a schematic it will take 4 or 5 hours.

I'm amazed too by my situation but not in a good way.
Hiwatt or Fernandes Guitars the manufacturer of this amp told me they have no schematic for this amp and that's for sure.This in itself I can't believe.It's from 2004 this amp,
but that's the situation.
I have sent the tech people some emails with suggestions from here,but tomorrow I thinkI'll phone them and pick it up.
The amp was restored to the stock configuration,
which has increased the gain. I was told if it's a design flaw then forget it.
I just can't understand why this amp seems unfixable!
I'm in Lasalle Canada near Montreal. As for soldering, I certainly can do that.
But the voltages in this amp I don't think I want to mess with.
The tubes don't appear to be the source of the problem although one tube was bad.