Would this make my Hiwatt go kaboom?

[frank57]

I'm going to get a proper wire to short the stuff out and probe the grounds.
So I would clamp one side to the ground bolt and touch the ground connections with the other tip?

In the original mod, with v1 out, the gain worked as you describe and as it works now:
turn up beyond 3 and hum and buzz.
The second mod with v1 out, and two parts out, the gain pot wasn't distorting anything if I remember correctly.
Now the ground wires to v2 are not shielded. They are two separate wires.
V1 is shielded, with the shield going to ground.
I don't know if that was part of the original amp design.

Now I did find at least one guy on a forum, who had the same problem.
At low volume the amp sounds great, but turn it up and hum and buzz.

I'll scan in those ground wires so you can get a better look at them.

Let's see what happens with the grounds, hopefully something good.

[frank57]

Using the old lead from my old multimeter which has pins on both ends, I inserted one end inside an insulated alligator clip and clipped that to the ground bolt and probed with the other.

Pin 2 on v2 kills the hum and buzz dead.
Pin 7 kills a lot of it , but there is still some hum and buzz there.
Also pin 2 on v4a kills the hum and buzz as well.
R6 C7 R8  c6 all kill the hum and buzz as well.
C6 seems to be working, there is 124 on one side and .oo4 the other .
Although that's no guarantee with this amp.
Shorting the .004 side kills the hum and buzz .
R5 and r7 I don't believe did anything although I could double check that.

Shorting the actual connection to ground of r8 though does nothing.
I didn't check any big caps mainly because I'm not sure how so better safe than sorry.
Shorting the parts around v1: nothing.
There also appears to be some wind like noise at times.
The gain pot is also very noisy.
As before radio on pin 7 of v2.

[frank57]

Would it make it sense to go into the tone stack from the cathode on v2a?

[Shrapnel]

The tone stack lies AFTER v2 (Well, it's on the output of V2 pin 1) Since pins 1, 2, and 3 are part of the same triode section, when you shorted pin 2 to ground and killed all the noise, the tone stack and V4 are not the problem areas. Your problem area seems to center around the gain pot or v1. everything else in the signal chain before that isn't injecting the noise. The noise is getting in on pin 7 mostly and leaking in slightly on pin 2 of V2. Your shorting of those two pins is the evidence, concentrate on that area and ignore everything else for the moment.

Let me ask again as I you hadn't really answered the question before, I'll make it easy.

Is the noise loud with the gain pot turned all the way down? (fully counter-clockwise) yes or no?
Is it as quiet as when pin 7 of V2 was shorted to ground, with the gain pot turned all the way down? yes or no?
Does the noise get louder when you turn up the gain pot (turn it clockwise)? yes or no?

[frank57]

Is the noise loud with the gain pot turned all the way down? (fully counter-clockwise) yes or no?

No, primarily less buzz.All controls at high noon.There isn't as much buzz there.
But loud hum, getting louder as you turn the master up.

s it as quiet as when pin 7 of V2 was shorted to ground, with the gain pot turned all the way down? yes or no?

I would have to say yes and no: it's similar but somewhat louder. I could check again.
It's definitely not the same as shorting pin 2 that's for sure.

Does the noise get louder when you turn up the gain pot (turn it clockwise)? yes or no?

Yes, does it ever.
Primarily an extra buzz that increases in volume.
Also some instability with the gain. Wind noises and so on.
I do have a sound clip but I don't know how to post it.

[Shrapnel]

Ok.

Turning the gain/volume ALL the way down may not give exact performance as shorting pin 7 as the pot there may not zero out (not a rare occurrence.)

This basically says all the noise has origins or signal injection in between the input jack and V2, with maybe a tad bit sneaking in between halves. IGNORE the rest of the amp for the most part. The Buzz may be helped with a grid resistor, but... it would have to go directly on pin 7 to be effective.  Check those traces around V1 and V2 closely to make sure that they are correct (no solder bridges, and bridges reconnecting cut traces where traces were meant to be connected.)

Did you ever chopstick the wires connecting the two boards? primarily on V1 and V2?

I'd think strongly of looking at that gain/volume pot closely too as it may have bigger problems than not zeroing out when turned all the way down.

[frank57]

Well, you definitely have the two traces with solder there.
It looks like they put some wires to bridge the gap over aluminum foil(?) that was placed there,
to cover the gauge in the board going into  pin 7 on v2.
On the other trace where 1m is it looks like theyy used a lead to bridge over the gap and solder.

But the problem was there with the traces cut as well.
A grid stopper didn't do anything.
It increased the buzz.
I think I'm going to replace that pot and see if that helps at all.

[frank57]

I changed the gain pot to the old one but there was not much change.
Less pot noise.
The minute you use the gain you get that buzz.
The radio seems to be sneaking in there in the background at a low level.
I changed v2 to a tungsol gold pin for a quick test and it seemed to eliminate the windy sounds.
So maybe these tubes are starting to go.
Like I said the high heater voltages are eating them up with limited usage at that.
What can be done to get the heater voltage to a normal level?
I started a thread on it but I'm not quite sure what to do there.
I tried chopsticking those wires on v1 and v2 and nothing seems to happen.
Maybe something with the buzz on v1, but hard to tell with the buzz through the roof like that.

Other question what should the voltage be on pin 2 of v3?
Would it be a good idea to try a 470k resistor into that grid pot at some point?

I did try the jet city combo and it was good.
Clean is alright. Gain on 2 MV on 6.
Reverb is not a surf style over the top but was nice and warm.
Not as high gain as a typical soldano .
A decent amp for the price.
Better with humbuckers I would say.
There is noise when you put the gain up and master up but nothing like this amp.
I'm sure dc power could kill a lot of that.
But I think the transformers on this Hiwatt are at least 50 % percent bigger and are doing something.g.
This Hiwatt sounds big at low volume, and even bigger when you turn it up but of course hum and bzzz.

[Shrapnel]

The grid blockers would be best mounted to the tube socket pins, and that PCB for those tube sockets is just too small to really put them in properly.  It looks like a wire is ran directly to pin 7 of V1 and putting that resistor in between those connections, AS LONG AS it still gets that grid resistor from the main PCB and signal from the jack. Problem is... no good way to connect it. If it can be done right, that will be the end of the amp playing radio receiver.

(Personally, considering the history of PCB mounted sockets, I'd be tempted to rip that tube PCB out, mount real sockets to the chassis, and wire them up properly. That would also allow grid blockers where they belong.)

[frank57]

would putting it on the jack do anything at all?
What should the resistance to ground read on the grids of v2 if I measure them?
Should it be close to zero?

[Shrapnel]

would putting it on the jack do anything at all?
What should the resistance to ground read on the grids of v2 if I measure them?
Should it be close to zero?

Grid blocker at the jack? Ineffective. Grid blocker ON pin 2 or 7 then connecting to the input signal? Very effective for that particular half of the tube.

Resistance to ground on V2: Pin 7, depends on the setting of the gain pot. (approx. 0-500K), Grid 2: IRRC, 470K (I'm not looking at the schematic.)

On pin 7 of V2 with the gain control turned all the way down it should be close to 0R. If all the way up, it should be at least 500K, maybe a bit more.

[frank57]

Here's Paul Ruby's idea for the board idea.
Looks like there's a bias pot there too.
Also trying to reduce the heater high voltages.
The diodes on the main pcb would come out too right?

Would reducing r8 to 100k or r17 to 10k do anything?

[Shrapnel]

Here's Paul Ruby's idea for the board idea.
Looks like there's a bias pot there too.
Also trying to reduce the heater high voltages.
The diodes on the main pcb would come out too right?

Would reducing r8 to 100k or r17 to 10k do anything?

WHY are you poking over there when it's clear that somewhere between the input jack and the input on pin 7 of V2 is where your noise is?
(Bad V1 ground? bad wires to/from V1?

I can understand the deal about the heater voltage, but as far as I can tell from this whole conversation, everything from V2 to the speaker is working correctly.

Playing with the grid resistor of a tube section that is known by this whole conversation as being perfectly fine or playing with  r17 has nothing to do with the noise.

[frank57]

You're right.
Someone was telling me the circuit was poorly designed
and that v1 was too strong for it and so on.That may be true but the real problem is elsewhere.

I think Paul's board idea will help overall.
Moving those hv wires and first filter cap out of there will help things.

Maybe I should redo the ground wires on v1 the way they were?
That shielded wire I'm sure was not there.
Could it be a hardware problem?
Socket itself?
Other oddball thing is the jack itself.
The tabs are reversed on it.
They close on the left not the right.
Where on earth they found these jacks and why did they use them is beyond me.
When I pull the guitar cable out the noise stops, until I move the controls again,
then all the noise is back.On the jet city amp I tested that did not happen at all.
That amp was very quiet with nothing in there and moving the tone stack.

I do have new jacks that fit, but because of the directional aspect I don't think they'll work.
I'll try it anyway.

Could the problem be right at the front of the amp at the jack itself?
Acting as a reciever because of the placement of the first filter cap and diodes?

Also a scan of the v1 ground wires.
The connector is soldered to the wire.

[Shrapnel]

You're right.
Someone was telling me the circuit was poorly designed
and that v1 was too strong for it and so on.That may be true but the real problem is elsewhere.

I think Paul's board idea will help overall.
Moving those hv wires and first filter cap out of there will help things.

Doubtful. IF they were adding noise when you shorted out pin 2 of V2 the noise would be present. Similar to the difference you described between shorting pin 7 and pin 2 of V2. But would still be there with the shorting of pin 2 (just lower yet.)

Maybe I should redo the ground wires on v1 the way they were?
That shielded wire I'm sure was not there.
Could it be a hardware problem?
Socket itself?

Returning EVERYTHING to stock may help.  The problem could be the socket, could be the wires, could be the connectors, could be all the modding, could be all the opinions making it worse. TOO MANY variables as-is. I imagine with the ground connectors there for the connection to V1 that there were wires that required ground shielding, more than likely two wires since there are two pads for the ground connection (probably plate and grid.)

A lot of people have opinions on what makes a good amp, and what makes a horrible amp in design and/or tone. Sometimes they're right, sometimes they've bought into the mojo voodoo, sometimes they're wrong, and sometimes they don't know jack about what they're talking about. I know practically everyone here doesn't buy into the mojo voodoo, but everyone here is still human and can be wrong from time to time. Those who don't know jack here usually don't post, and just follow to learn if interested in the thread. Those who know, may just follow to see the debug process in action to make sure it's going right. I can't say that for other boards as I don't frequent them because I've got a great knowledge base here to help me learn what I still don't know. I'm sure though you've seen threads elsewhere that was just a debate of this amp's crap or this amp is the god of all amps and all the fighting that ensues.

Let's for the sake of sanity not go chasing red herrings and focus on the noise problem and eliminate the possible causes in that locale before we go looking outside of it as most problems are isolated to one area.

Other oddball thing is the jack itself.
The tabs are reversed on it.
They close on the left not the right.
Where on earth they found these jacks and why did they use them is beyond me.
When I pull the guitar cable out the noise stops, until I move the controls again,
then all the noise is back.On the jet city amp I tested that did not happen at all.
That amp was very quiet with nothing in there and moving the tone stack.

OK, This is new info for me. Noisy with the guitar plugged in, quiet as soon as unplugged until you move knobs. It's sounding more and more like a ground problem to me, possibly a small fracture on a ground trace or a poor ground connection.

I do have new jacks that fit, but because of the directional aspect I don't think they'll work.
I'll try it anyway.

For the way it mounts and connects, the existing jack looks right. This might have been a deal of "make it different so they have to get it at a premium price" or "to make it work the way we want, we need it reversed." I wouldn't quite mess with the jack yet.

Could the problem be right at the front of the amp at the jack itself?
Acting as a reciever because of the placement of the first filter cap and diodes?

The jack itself has nothing to do with the radio reception problem. Anyone here can verify that. All amps that don't have a grid block resistor on that first input are susceptible to picking up radio.  The jack may add to other noise, but as a direct cause (as in, just replace it = no more radio) it is not.

[frank57]

There are two wires for the plate on v1 one signal and one ground.
The ground is not a shield though just a regular wire.
I'm wondering what they did on the original mod to get the signal to v2 too if it might help.
They must have had more than one wire.
They cut the two grid traces on v1 and v2 but then what?
Whoever did it must have seen the problem was from v1 to pin 7 and tried to get around it.
But it did not work.

I'm going to try an experiment and put back that wire connecting the jack
 to the gain pot and see what happens hum wise.
Anyway to troubleshoot the grounds better?


One guy I found on a forum had a hum increasing with the mv problem on a marshall.
Now this fellow had a scope and a lot more knowledge.
 In his case it was a ground on a filter cap.
Now how would I check those filter caps?

I do have some shielded wire coming in .
Maybe take those two grounded wires on v1 and avoid
 the connectors all together, go straight to the pads from the tube pins and see if anything happens?

One other thing that may be doing something are the voltages.
You can see some of those resistors are being pounded above 350(1/2 watt resistors).
Especially around the phase splitter and 4b
which had too high plate voltage at one point.
I replaced the resistors and it's working fine for now.
But I think over time those resistors end up not working properly.
Some I beefed up to 1 watt along the b+.
The screens too are getting pounded pretty good.


 

[frank57]

 Just a quick note.
I did a bit more troubleshooting.
Shorted to ground pin2 of v2 hum and buzz went down as before.
It seemed quiet but..
this time I also moved the red hv wires with a chopstick and
the amp got a lot quieter.
At least another 35 -40 %.
So those wires are definitely worth getting out of
that mess in the middle of the pcb for sure.

[frank57]

So I reattached a connector to that wire on pin 7 v1 and put it in the plastic header
on the tube pcb.
Keeping it shielded on one end as before.
Also put in some 1 watt resistors at the phase splitter and screens.
I also moved the ground wire of the jack to the lug closest to the ground bolt,
although I had it at this lug before at times.

Now when I short those parts around v2 like before, I kill the hum and buzz
and the tone controls don't bring it back.
But not the grounds of those parts.
So the 223 cap ,330 k resistor, 470k and 470 pf all kill it.
The cap on v1 does nothing.
Before I was changing the frequency.
Why is that now?
As before I get the radio on pin 7, v2 pin 2 quiets things down.
Also on r22 220k there are 68 volts on either side not zero like in the previous post.
Is that right?

Also with nothing plugged in, and everything at zero there seems to be a bit of a low level hum.
Update on that:
The shield on the grid wire was giving continuity on my tester.
This caused the hum and the volume to go down and stopped the jack from working properly.
I fixed that and we're back to the original problem.
So going straight to the grid pin on v1 as opposed to the connector doesn't seem to make much difference.
I'm leaving the connector on since this makes working on the amp easier.
Moving the red hv wires also makes everything quieter.

[frank57]

Could part of the problem here be the type of connector wires used on the grid of v2?
In actual fact it's  3  wires inside a shielded covering.
What exactly would the shield be doing?
Only two wires are actually being used though.
There is a red and white wire in there and a bare stranded wire it looks like.
That's what's being used to ground.
Any possible problems that could arise here?
Same thing with the plate wires on v1 and line out.

Why not just use rg174u?

[rundle61]

hi trying to find out why my Hiwatt t20 has started to cut out,it works but now and then fades out and and i loss signal,i still get slight cracklel if i move master vol a little.if i turn it off and leave a while it comes back working, only does this intermittently which is rather a pain as you have no idea when it will happen next ,hope someone can help

[HotBluePlates]

... started to cut out,it works but now and then fades out ...

It's better to start a new thread, talking only about your amp.

"Cuts out" and "works, but sometimes fades out" sounds like an intermittent connection.  The first place you have access to is the jack you plug your cord into the amp, and the jack you plug the speaker into the amp.  Those should be solid, not loose or wiggly.

The other thing you have easy access to is the tubes themselves.  Do the sockets grip the snugly, or are the loose & come out easily?

There may be other connections inside.  Cables from sockets to p.c. board, or board to jacks, etc.  Inspect those to be sure of solid connection.

Beyond that, you may need help of a tech.  If it's not something a user can touch from outside the amp, it may not be safe (or you may not have the tools to check what's happening).