Hot Rod Deluxe mods

[Mark]

A friend of mine has a HRD that he has had for ages.
The thing I HATE about this amp is the linear master volume control. It’s a cheap shot to make the amp seem louder. Years ago the friend said it was only on “2” and I pointed out it only sounded fatter when turning it up.

So the master volume pot is a no brainer for replacement with a log pot (if I can find the Fender part number).

However, there are a whole lot of component choices I wonder about.

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In the first stage, I thought the 47uF cathode bypass cap was a bit excessive though it might be that value to stop signal bleeding through.

I thought the 1.5nF value was small, a typical value is 4700pF and the Mesa Boogie Mark 1 amps used 0.01uF. I have seen people complain that the drive channel has too much drive, changing the series 100K resistor to something larger would be a better solution to the internet touted 12AT7 solution.

Thoughts?

[Mark]

But wait there is more.

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Looking at the tone stack, you would think this amp is very bass heavy. There is the 130K slope resistor which I would lower to 100K. The 220K resistor hanging off the bass pot seems to be there to minimise the effect of the bass pot, I think I would get rid of that as you can always turn the bass down. The mid pot can have the wiper bridged across too if desired. Bill M was fond of it.
I’m a fan of silver mica treble caps, so that would go in.

[Mark]

Getting bored, there’s more coming.

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This is part of the more drive circuit. It’s basically the same as the treble boost (0.68uF versus 1uF). I understand 5uF might be a bit much, but 2.2uF would have to be a better value?

It would let more mids through.

[Mark]

Let’s move on

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As stated the master volume pot is a no brainer, it has to go.

However, I do wonder about the 390pF cap across the master volume pot. So much seems to be done earlier in the amp to ensure it’s bright.

I also find the 0.047uF cap values for C2 and C10 a bit strange given the efforts to reduce bass response earlier in the amp. Surely, 0.022uF would have been fine, I realise that I probably wouldn’t hear the difference between 0.047uF and 0.022uF.

The 22uF “more drive” cap on the cathode of V2B seems an overkill, surely a value up to 5uF would suffice?
The idea of using a cathode resistor value greater than 1.5K is appealing. Something around 2.2K is appealing.

Thoughts?

[Mark]

Nearly at the end, wait for it.

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This mod has been mentioned before. People have thought the reverb is a bit too in your face with these amps.

Removing R103 and C52 would change this. The other option would be to increase R103 from 1.5K to suit one’s expectations.

[Mark]

This is it.

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The Tweed Bassman P.I. stage has quite a bit of output, given that everything happens in the preamp, perhaps a 12AT7 or taming the circuit somewhat might be appropriate?

Thoughts?

Thanks for your time and patience.

[bepone]

all this pointed out is tone shaping , an someone in Fender chose this values. You can do your preference, why not.

It is pcb job so will make all those mods and testing/retesting difficult, and too much time consuming at the end (10% of modding, 90% of time mounting /dismounting) what will kill all of the fun part.

[Dr Tony Balls]

Complete gut renovation.

[LOUDthud]

Complete gut renovation.

Great job !

Anybody know where to get a chassis to fit one of these ? I got a cabinet with speaker cheap before I figured out no standard tweed chassis will fit

[Colossal]

Ahhhh....that redo is SO much better. Nicely done.

[Dr Tony Balls]

Complete gut renovation.

Great job !

Anybody know where to get a chassis to fit one of these ? I got a cabinet with speaker cheap before I figured out no standard tweed chassis will fit

I'd just have one made. There's an active thread about custom chassis builders. I use Synaptic amps, though it seems like their current communication levels might be delayed.

[Mark]

Complete gut renovation.

So there is a lot less controls and circuitry, what went and what stayed?

[Mark]

all this pointed out is tone shaping , an someone in Fender chose this values. You can do your preference, why not.

It is pcb job so will make all those mods and testing/retesting difficult, and too much time consuming at the end (10% of modding, 90% of time mounting /dismounting) what will kill all of the fun part.

I think you have to start with listening to the amp an knowing what it does well and what needs improvement. The idea was to start with possible mods and discuss experiences with people who’ve been down this path before.

Fromel does a kit for these amps. Bear in mind the Deluxe and DeVille are basically the same amp with different power supplies.

According to the link, it’s replacing the plate resistors with higher wattage components. Increasing the screen resistors from 470 ohm to 1K (the Deville has a 50V higher rail voltage which would necessitate this mod). The power supply cap values remain the same. Better caps in the tone stack but original values though 0.047uF may be an option (I don’t understand why the tone stack caps are so important?)

The slope resistor is dropped from 130K to 100K though the link implies 56K may be an option which will load down the previous stage.
The input cap the the P. I. Is reduced from 0.022uF to 0.01uF.
The cathode bypass on the first stage goes from 47uF to 22uF (given all that’s done to reduce the bass response in the amp, I’m surprised this isn’t as low as 5uF).
The first cathode resistor is lowered from 1.5K to 820 ohm, I’m a little surprised by this change.
The 390pF cap across the gain master volume is removed.
The 220K resistor from the bass pot to earth is removed.
The last option appears to be a more Marshall like tone stack.

I think most of the mods are correct but some of the mods don’t line up with the components pictured.

https://forum.pedalpcb.com/threads/fend ... ist.10007/

https://www.sweetwater.com/insync/mods- ... od-deluxe/

https://www.tangible-technology.com/sch ... /hrd-1.htm

https://youtu.be/au8S5RNOTUg

https://youtu.be/n_Y5XPhTTkQ

[Dr Tony Balls]

Complete gut renovation.

So there is a lot less controls and circuitry, what went and what stayed?

What went: Everything except the chassis and the iron.

I'm being jokey putting that in this thread because its not really a mod, just a replacement.

[Reeltarded]

Where did all the stuff go!!?