Here is a link to an older thread for a Lead 30 I built from an almost impossible to find schematic. There is a link inside the thread to a mislabeled schematic which is actually a Lead 20. I added the extra pair of 6bq5's to raise the output to a quad for a 30 watter.
http://ampgarage.com/forum/viewtopic.ph ... c&start=15
California Hiwatt "Lead 30"
Moderators: pompeiisneaks, Colossal
California Hiwatt "Lead 30"
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Forrest Gump
Forrest Gump
Re: California Hiwatt "Lead 30"
It's not a lead 20 schematic it's a schematic for the Korean Custom 20 tube,
an amp full of design errors.They were modded by Fernandez to try to solve the design goofs causing hum and buzz with 2 15k resistors on the cathodes.Turned up they are really noisy.Some also had low pass filters installed to filter out the buzz.
The lead 20 from what I have seen of it is slightly different as is the lead 30.
Also note the 56k resistor.
The lead 30 uses 47k.
470k is pushing your luck.
The lead 20 has the Hiwatt tonestack and I believe no cap on the second stage
same with the lead 30 although I can't be 100 percent on that as there is a small cap at the front of the lead 20 but I believe that's for interference.
the lead 30 has a slightly different power section as well.22k resistors on the tube grids.
These amps can be figured out pretty quick with some more photos.
In both cases I believe there is no cathode cap on the second stage.
Looks like the lead 30 has the same .0022 resistor on the tube socket from pin 2 to 3.
an amp full of design errors.They were modded by Fernandez to try to solve the design goofs causing hum and buzz with 2 15k resistors on the cathodes.Turned up they are really noisy.Some also had low pass filters installed to filter out the buzz.
The lead 20 from what I have seen of it is slightly different as is the lead 30.
Also note the 56k resistor.
The lead 30 uses 47k.
470k is pushing your luck.
The lead 20 has the Hiwatt tonestack and I believe no cap on the second stage
same with the lead 30 although I can't be 100 percent on that as there is a small cap at the front of the lead 20 but I believe that's for interference.
the lead 30 has a slightly different power section as well.22k resistors on the tube grids.
These amps can be figured out pretty quick with some more photos.
In both cases I believe there is no cathode cap on the second stage.
Looks like the lead 30 has the same .0022 resistor on the tube socket from pin 2 to 3.
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Re: California Hiwatt "Lead 30"
I appreciate the info and also the time you put in finding all this out. As you know Sterling Imports was really a "flash in the pan" so to speak and it's hard to even prove they were in business they went out so fast. I see on a couple other sites your looking for pcb photos of the lead 30 and if still I will link you to these
http://s871.beta.photobucket.com/user/s ... ?start=all
This guy may even be willing to take more. Originally when I fired up this prototype of mine it sounded bad. I'm sure I subbed in the tonestack and PI out of the classic Hiwatts and it perked right up. My brother has the amp now and he loves the gain. I like rolling off the gain and cranking the master. If it's no bother I'd enjoy hearing anything if you continue your quest. For what it's worth , this little amp really kicked some major butt. It'd be a shame to see it go.
http://s871.beta.photobucket.com/user/s ... ?start=all
This guy may even be willing to take more. Originally when I fired up this prototype of mine it sounded bad. I'm sure I subbed in the tonestack and PI out of the classic Hiwatts and it perked right up. My brother has the amp now and he loves the gain. I like rolling off the gain and cranking the master. If it's no bother I'd enjoy hearing anything if you continue your quest. For what it's worth , this little amp really kicked some major butt. It'd be a shame to see it go.
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Forrest Gump
Forrest Gump
Re: California Hiwatt "Lead 30"
shouldn't the loop be like this ??...........2651amp wrote:It's not a lead 20 schematic it's a schematic for the Korean Custom 20 tube,
an amp full of design errors.They were modded by Fernandez to try to solve the design goofs causing hum and buzz with 2 15k resistors on the cathodes.Turned up they are really noisy.Some also had low pass filters installed to filter out the buzz.
The lead 20 from what I have seen of it is slightly different as is the lead 30.
Also note the 56k resistor.
The lead 30 uses 47k.
470k is pushing your luck.
The lead 20 has the Hiwatt tonestack and I believe no cap on the second stage
same with the lead 30 although I can't be 100 percent on that as there is a small cap at the front of the lead 20 but I believe that's for interference.
the lead 30 has a slightly different power section as well.22k resistors on the tube grids.
These amps can be figured out pretty quick with some more photos.
In both cases I believe there is no cathode cap on the second stage.
Looks like the lead 30 has the same .0022 resistor on the tube socket from pin 2 to 3.
You do not have the required permissions to view the files attached to this post.
Re: California Hiwatt "Lead 30"
If memory serves me , I had to modify this loop because of it's inability to achieve the proper drive voltage for the outboard effect. I actually put the resistors on the return side as it was causing the issue on the send side of the loop.. Why Sterling imports didnt use a cathode follower before the stack or the loop is beyond me. I may experiment with this one day.
I am backwards sorry. I moved them over to the send side because my drive voltage was to much for my outboard gear
I am backwards sorry. I moved them over to the send side because my drive voltage was to much for my outboard gear
Last edited by passfan on Sun Jan 13, 2013 12:36 am, edited 1 time in total.
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Forrest Gump
Forrest Gump
Re: California Hiwatt "Lead 30"
Fernandes put it out .
I'm not surprised it didn't sound good.
If you follow the board values the gain is too strong and you lose the note definition.
It's interesting and packs a wallop at low level, but once you play on a better amp you realize the circuit is too much.
That's probably why it was modded to 15k on the cathodes which improves it but it's still a dubious circuit.
There were also filters in there to filter out the buzzz.
I f you start to follow the lead 20 and lead 30 and take off that cap on the second tube
it starts to work.If you bypass the loop which in the amp is amplifying the bzz from the preamp,then you have 3 stages in the front and it starts to work a lot better as well.
How does it sound with the Hiwatt tone stack?
Right now I'm not sure what to do with it.But I might try the lead 20 lead 30 preamp and see how it flies.
the efx loop is a problem because it's amplifying bzz from the preamp.
The buzz I think is from a poor transformer setup.
From photos I've seen the lead 30 and lead 20 both have a 2200pf cap or .0022 on the first tube going from pin 7 to pin 8.
I'm not surprised it didn't sound good.
If you follow the board values the gain is too strong and you lose the note definition.
It's interesting and packs a wallop at low level, but once you play on a better amp you realize the circuit is too much.
That's probably why it was modded to 15k on the cathodes which improves it but it's still a dubious circuit.
There were also filters in there to filter out the buzzz.
I f you start to follow the lead 20 and lead 30 and take off that cap on the second tube
it starts to work.If you bypass the loop which in the amp is amplifying the bzz from the preamp,then you have 3 stages in the front and it starts to work a lot better as well.
How does it sound with the Hiwatt tone stack?
Right now I'm not sure what to do with it.But I might try the lead 20 lead 30 preamp and see how it flies.
the efx loop is a problem because it's amplifying bzz from the preamp.
The buzz I think is from a poor transformer setup.
From photos I've seen the lead 30 and lead 20 both have a 2200pf cap or .0022 on the first tube going from pin 7 to pin 8.
Re: California Hiwatt "Lead 30"
I wound up closer to the 2 input early 80's preamp and the difference between tone stacks was noticeable. It does have way to much gain which my brother loves as he can have his singing leads at sub hearing levels. With two young children he rarely gets to play if it isn't late at night. It is a nice sounding amp and everyone who plays it loves it. I built it as a combo with a ported G12-65. It started out sealed but had no bottom end until I drilled a 4" hole to port it , then it came to life. It reminds everyone of the Marshall MV style amps after they modded the preamp for more gain. Try a different tone stack and possibly dump the send , it's useless anyway. A standard PI may work wonders as well. I'm not sure how much the regulation affects the tone there as I never tried it without. It is too much gain for me , which I just dial out. With the preamp volume down and the master up it gets loud , clean , and punchy like the older Hiwatts were known for. Once you're there just dial back in the gain you want.
"It Happens"
Forrest Gump
Forrest Gump
Re: California Hiwatt "Lead 30"
I'm not quite sure how to rebuild it so I would have to get the Oconnor book which might help if I go that route.Was it tough to rebuild at all?
You know far more than I do.
I did try a low gain version which actually was quite interesting.
Have you seen the sa210 schematic?That could be an interesting amp for you.
How did you do the efx loop?
I'm trying to do the hiwatt tone stack on the pcb but it's a little tricky to implement it.
I have to take one pot off the pcb.So far it hasn't worked.
One other thing they did on the custom 20 tube was they ran the phase splitter too clean.They took the power from the back of the amp with higher voltage.
On the other designs it's fed from the front.
You can see on the lead 20 pcb how all the Hiwatt values are there.
No cap on the second tube.That will probably work.
Now on the fernandez one the way they mounted the transformers might be a big part of the buzz problem.
The low gain version sounds like this:
http://www.mediafire.com/?0f4ela4im33a6eb
I had to hit it pretty hard just like the real Hiwatt.
You know far more than I do.
I did try a low gain version which actually was quite interesting.
Have you seen the sa210 schematic?That could be an interesting amp for you.
How did you do the efx loop?
I'm trying to do the hiwatt tone stack on the pcb but it's a little tricky to implement it.
I have to take one pot off the pcb.So far it hasn't worked.
One other thing they did on the custom 20 tube was they ran the phase splitter too clean.They took the power from the back of the amp with higher voltage.
On the other designs it's fed from the front.
You can see on the lead 20 pcb how all the Hiwatt values are there.
No cap on the second tube.That will probably work.
Now on the fernandez one the way they mounted the transformers might be a big part of the buzz problem.
The low gain version sounds like this:
http://www.mediafire.com/?0f4ela4im33a6eb
I had to hit it pretty hard just like the real Hiwatt.
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Re: California Hiwatt "Lead 30"
For starters I scratch built from the ground up. Prototype first in an old hammond chassis , refined the design , and then constructed with a turretboard in a big chassis just like Hiwatt England did. Could be why mine is kicking along pretty good. I can see it would be a pain trying to transform a pcb into something else. The effects loop deal I just played with the values in the resistor string just before the send to dump signal.
Have you tried a different speaker? Even when I had my old Lead 30 head I ran it through a Marshall 2x12 with 65's in it. My clone was a goat until I cut that port in the cabinet.
Have you tried a different speaker? Even when I had my old Lead 30 head I ran it through a Marshall 2x12 with 65's in it. My clone was a goat until I cut that port in the cabinet.
"It Happens"
Forrest Gump
Forrest Gump
Re: California Hiwatt "Lead 30"
Was the 470k resistor changed to 47k like on the Hiwatt ol?
What I found too was ditching the efx loop completely improved things right away.
Maybe this might work for the Hiwatt tone stack.
But this amp has a really poor pcb design and that's a problem straight away along with the hardware setup.A lot of hum was from the Power transformer and Hv wires over the tubes.What I might try is moving the transformers around and see if anything happens.
The voltages were at 7.8 on the filaments.
Once I lowered them with big resistors the hum quieted down from the Master.
Have you seen the dr210 schematic by the audio bros?I added some missing bits.
They also have dc power on the filaments.
Could be an interesting amp for someone to build.
What I found too was ditching the efx loop completely improved things right away.
Maybe this might work for the Hiwatt tone stack.
But this amp has a really poor pcb design and that's a problem straight away along with the hardware setup.A lot of hum was from the Power transformer and Hv wires over the tubes.What I might try is moving the transformers around and see if anything happens.
The voltages were at 7.8 on the filaments.
Once I lowered them with big resistors the hum quieted down from the Master.
Have you seen the dr210 schematic by the audio bros?I added some missing bits.
They also have dc power on the filaments.
Could be an interesting amp for someone to build.
You do not have the required permissions to view the files attached to this post.
Re: California Hiwatt "Lead 30"
As far as I remember it still has the 470k. 7.8 volts is too high. Does the filament winding have a center tap? If not you should be able to find a couple of resistors to ground providing the filament a reference. I just built an Express and it hummed and buzzed to get all until I remembers to put in those resistors. O 
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Forrest Gump
Forrest Gump
Re: California Hiwatt "Lead 30"
It has a center tap.
I tried 2 100 ohm resistors at one point instead.
It helped with the hum but added hiss.
I also tried diodes to lower the voltages.
2 X 10 watt .22 wirewound was the quieter route to go.
The hum isn't really the biggest problem.
The buzz is coming in at the input (a 102 cap to ground stops that but reduces the highs too much)and in the second stage somewhere.It goes up as you turn the gain.
The PT is playing a role in the whole problem.
The transformers are both parallel with the endbells facing each other.
My guess is there is some kind of coupling going on whether though the bad pcb layout or
the bad hardware layout.Turning the Pt affects the buzz making it go down some,
but the hum then goes up.
I'm not quite sure what to do with the amp at this point but moving the Ot around is one thing I might try.It should be rebuilt.
They also wired the fuse to the neutral which seems a bit odd.
I tried 2 100 ohm resistors at one point instead.
It helped with the hum but added hiss.
I also tried diodes to lower the voltages.
2 X 10 watt .22 wirewound was the quieter route to go.
The hum isn't really the biggest problem.
The buzz is coming in at the input (a 102 cap to ground stops that but reduces the highs too much)and in the second stage somewhere.It goes up as you turn the gain.
The PT is playing a role in the whole problem.
The transformers are both parallel with the endbells facing each other.
My guess is there is some kind of coupling going on whether though the bad pcb layout or
the bad hardware layout.Turning the Pt affects the buzz making it go down some,
but the hum then goes up.
I'm not quite sure what to do with the amp at this point but moving the Ot around is one thing I might try.It should be rebuilt.
They also wired the fuse to the neutral which seems a bit odd.
Re: California Hiwatt "Lead 30"
It could be that a better way to look at the phase splitter is like this.
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Re: California Hiwatt "Lead 30"
Scored a lead 30 combo with reverb off eBay. There were a couple of things wrong with it as far as previous tech work and wrong values. I found a schematic online and verified it with my amp and so I will post it up here as being verified. I changed my second gain stage to a cold clipper by swapping the 1.5 k cath resistor to a 10k . Made the overdrive much smoother and cleaner. 1st stage cathode bypass was changed from 150uf to a .68uf
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Forrest Gump
Forrest Gump