Completed Friedman PT20 Modded to Hopkins HPT20

[NewReligion]

All feedback welcomed Good, Bad & Ugly.

David...♫

 

[crankyrayhanky]

Dig it!
Sounds killer

 

[NewReligion]

Dig it!
Sounds killer

Thanks Ray. Took a couple days to calculate the sonic balance. Great experience for me.

I really appreciate the feedback.

David

 

[V2a]

Please consider this constructive criticism.

I think the video shows some misunderstanding of the basis for Friedman's signature sound, or at least the PT20's sound. It does not come from one "filter circuit" (which I presume is an interstage voltage divider with bright bypass cap) or "neutering circuit". If you don't already have a signal generator and oscilloscope, I suggest that you get these tools to help visualize what an amp is doing. I also suggest you think a bit more about circulating currents as opposed to just voltages and filter cutoffs. These will give you a better understanding of what an amp is actually doing and perhaps even why the designer of the amp made certain decisions. A builder could copy an amp from a schematic and still not end up with what the designer intended. This is particularly true of Friedman amps.

And as a checky parenthetical comment, I don't think you need a serial number for changing three parts and adding a clipping circuit

 

[NewReligion]

Please consider this constructive criticism.

I think the video shows some misunderstanding of the basis for Friedman's signature sound, or at least the PT20's sound. It does not come from one "filter circuit" (which I presume is an interstage voltage divider with bright bypass cap) or "neutering circuit". If you don't already have a signal generator and oscilloscope, I suggest that you get these tools to help visualize what an amp is doing. I also suggest you think a bit more about circulating currents as opposed to just voltages and filter cutoffs. These will give you a better understanding of what an amp is actually doing and perhaps even why the designer of the amp made certain decisions. A builder could copy an amp from a schematic and still not end up with what the designer intended. This is particularly true of Friedman amps.

And as a checky parenthetical comment, I don't think you need a serial number for changing three parts and adding a clipping circuit

But of course you know exactly what I did with only 3 components. That in it self is constructive lol.

I used an oscilloscope, often do. Your presumption on filtering is way off. There were a number of changes in the amp in addition to development of assemblies to open it up then reach a well scoped analog saturation. True the clippers are bells and whistles but still your remarks are well received.

I accepted the challenge from the owner who is now pleased with the HPT20 as it is heavily modded in the preamp.

I had to change the OT primaries of the EL84 pin 7’s in order to make a NFB Presence Control work. I now know why most 18 watt amps do not use a NFB circuit as the EL84’s are easily pushed into clipping.

I own a couple BE 100’s which IMO had the same blanketed Friedman affect which has been lifted. I meant no disrespect to Dave Friedman but your comment eluding to what I did was novice & created an unstable circuit was unwarranted as you have no idea what work has been accomplished.

For my client, (who has been employed deep in the guitar business for over 25 years with a huge respected company) this is a vast improvement. As I have thick skin, I know what I am doing, I thank you for the Good, Bad & Ugly.

The HPT & 001 was requested by the owner as I obviously voided any warranty lmao.

I really love seeing those Cameron modded, Friedman modded Jackson modded Marshall’s on eBay.

Perhaps neutered was a poor choice of a description to repeat as I do respect Dave’s ground breaking work just as I do any other that can build a well balanced stable high gain circuit which IMO is much more difficult than a clean circuit.

I stand by my statement that the PT20 provides a great platform for others to build upon just as the Marshall 1987/1959/2203/2204 do.

Thanks again for the feedback & constructive criticism and best to you V2a.

David

 

[V2a]

You are reading a bit too much into my post, NR. I did not imply that what you did led to instability etc. (although now that you alerted me to an added NFB loop, I hope you calculated open- and closed-loop gains of the PI, output tubes, and OT; without doing that, instability is quite possible).

I didn't actually say you were a novice, but that's probably fair to say - especially when people like Dave Friedman are the yardstick. As you said, modding the PT gave you a great learning experience. BTW - EL84s were designed to drive a speaker with a much smaller input signal so that people could build and sell radios with fewer preamp tubes (and also stock only 9-pin sockets). Hence 84s can sound harsh, not only with NFB (there are cures for that) but also with multi-stage preamps. Some builders (Bruce Collins of Mission Amps being one that comes to mind) refer to distorted EL84 sounds as a can of buzzing bees. Dave did a good job of keeping those bees at bay. There are many other tricks that can be applied too.

 

[NewReligion]

You are reading a bit too much into my post, NR. I did not imply that what you did led to instability etc. (although now that you alerted me to an added NFB loop, I hope you calculated open- and closed-loop gains of the PI, output tubes, and OT; without doing that, instability is quite possible).

I didn't actually say you were a novice, but that's probably fair to say - especially when people like Dave Friedman are the yardstick. As you said, modding the PT gave you a great learning experience. BTW - EL84s were designed to drive a speaker with a much smaller input signal so that people could build and sell radios with fewer preamp tubes (and also stock only 9-pin sockets). Hence 84s can sound harsh, not only with NFB (there are cures for that) but also with multi-stage preamps. Some builders (Bruce Collins of Mission Amps being one that comes to mind) refer to distorted EL84 sounds as a can of buzzing bees. Dave did a good job of keeping those bees at bay. There are many other tricks that can be applied too.

I read little into your post. You assumed far too much as you still do. This details a certain recessive trait in ones critical thinking or perhaps character. I personally find your opinions limited in depth if not one sided as there are many ways to skin a cat properly by thinking outside of the box as my accomplished mentors have taught me.

Your quips are funny which is where many insecure minds hide. Good, Bad & Ugly are fine but you offer little of substance in assistance rather you seize any opportunity to be the class clown.

I think it best that we refrain from each others post's as to keep this community a better place and one of productivity in order to minimize the professional trolling.

And yes, this was a wonderful experience and exercise in working with my first of many to come 18 watt circuits. I learned much from the NFB I balanced and decided against.

I am quite certain I have been clear as I want no misunderstandings. Too bad we are off to a bad start as your work sounds good.

Regards, David...♫

V2

 

[V2a]

You asked for input and you got it. You said you had a thick skin, and then you lash out again and again. It's clear from your posts that you are insecure and need praise. Not a thick skin at all.

In short - you are the new Billy Blades without the run on sentences (but certainly run-on posts).

 

[NewReligion]

You asked for input and you got it. You said you had a thick skin, and then you lash out again and again. It's clear from your posts that you are insecure and need to praise. Not a thick skin at all.

In short - you are the new Billy Blades without the run on sentences (but certainly run-on posts).

You edited your original post in which you arrogantly commented about changing only 3 components. Let’s not pretend you did not make that smart ass comment dressed up like the rebuke it was.

Billy Blades lmao, that’s all you have? Indeed, you lost your eloquence and I thought you were at least an articulate troll. Apparently falling short there as well.

I asked you to stay off of my post’s as I wish to remain professional and not disrespect your “work” or practicing guitar strumming.

Your regurgitation of superfluous information is not supported by your works I found on YouTube. I do not wish to belittle your ability or inability as I know you play your best so please go elsewhere to troll.

Don’t go away mad, just go away.

 

[V2a]

NBB - you are loosing the battle with your own sanity, my friend. The three-resistor comment appears in the last sentence of my unedited first post.

You make lots of wrong assumptions about the people with which you interact online, mainly because you are only interested in yourself and don't take the time to get to know others. If you ever want to get together to see who has the sharper mind, just let me know!

 

[V2a]

I'll leave it to you to have the last word. Take care.

 

[NewReligion]

NBB - you are loosing the battle with your own sanity, my friend. The three-resistor comment appears in the last sentence of my unedited first post.

You make lots of wrong assumptions about the people with which you interact online, mainly because you are only interested in yourself and don't take the time to get to know others. If you ever want to get together to see who has the sharper mind, just let me know!

Indeed it was the last line. I have been awake for 43 hours. It’s not people, it is you. As for sharp? We just did that. I would be accused of beating on a handicap. We can study, learn, understand and apply our talents but if a guy has a shit tin ear, then that can not be helped.

Best to you.

And now for a short intermission before we get back to the OP.

Since it’s all about me.

 

[CrazyNutz]

Sounding good.

@V2a You were pretty cocky in your criticism. Really unnecessary, seems like you were trying to start an intellectual challenge? The guy is learning, and quite frankly most of the stuff he's done sound pretty damn good. A good ear, determination, with some technical knowledge is all most the great amp builders needed to produce some of the best sounding amps. It's not all about being super technical.

 

[NewReligion]

Sounding good.

@V2a You were pretty cocky in your criticism. Really unnecessary, seems like you were trying to start an intellectual challenge? The guy is learning, and quite frankly most of the stuff he's done sound pretty damn good. A good ear, determination, with some technical knowledge is all most the great amp builders needed to produce some of the best sounding amps. It's not all about being super technical.

Hello CrazyNutz. Glad you enjoyed the modded tones. My mission statement is to bring the best tone I can to kindred ears. No Fizzyness, All Business.

David

 

[CrazyNutz]

I retract what I said to v2a. Clearly there was some history to this spat. I'll leave it at that.

 

[NewReligion]

 

[fusedbrain]

WTF happened there

It's too bad this thread has kinda "gone off the rails" so to speak, as I thought the modded amp sounded quite good, and I typically find the contributions to the forum from both V2A and NR to be of value and informative.
It would have been nice to have more of a discussion about the mods, the clipping circuit, the issues arising from adding NFB to an EL84 amp etc...
This is supposed to be the "Tech Corner" forum after all....

Oh well.... such is life on the interwebs in 2019

 

[NewReligion]

WTF happened there

It's too bad this thread has kinda "gone off the rails" so to speak, as I thought the modded amp sounded quite good, and I typically find the contributions to the forum from both V2A and NR to be of value and informative.
It would have been nice to have more of a discussion about the mods, the clipping circuit, the issues arising from adding NFB to an EL84 amp etc...
This is supposed to be the "Tech Corner" forum after all....

Oh well.... such is life on the interwebs in 2019

Hello fusebrain. I received a phone call from a prominent professional member of the world of music wanting to know if I could lift the dark sound (open it up Marshall-ish) and add more usable gain to this 18 watt amp. He named a few of the top hot rods he liked. I decided to take the job.

I reworked all preamp anodes, cathodes and couplers. In addition I created a couple assemblies to remain protected in heat shrink. Shunted voltages to ground in other places. The way I connected the different value couplers in combination with the anode values in series played a great part.

My past experiences aided in working outside of the box. I own 2 BE 100’s (2013 dual input & 2014 single input). Great amps as they were/are my live work horses when I don’t use my Marshall Pandora’s. Easily replaced if stolen. Dave uses a (voltage divider) 220k on the wiper of the BE 100’s I own. Reducing this value or even completely removing it not only increases volume as someone eluded to but allows the amp to react more like a Marshall tone stack.

On this PT20 the 220k voltage divider is located on the Master Volume. You can see the possibilities here using a on/off/on switch. I also used two different sets of clippers with my own choice of cap and resistor to offer distinctly different clipping flavors as requested by the customer.

I checked everything on the oscope to ensure stability and no crossover distortion when finished of course.

Just as importantly I used my ears to dial in what I found optimum for the Hopkins sound as we each seem to have a sonic place we like to end up. This ended up sonically much like my 50 & 100 watt Marshall modded Pandora’s.

You asked about the NFB and Presence.

This was my first experience on a 18 watt though I have thousands of hours repairing and modding larger amps.

I decided to try out a NFB and Presence Control. The PI configuration was a 100k/150k on anodes, 470 shared cathode and 27k tail.

I started with a 47k for a Presence resistor on a 5kL pot wired lol e a 1959 with a .1uf cap. I could not get a signal so I changed around the OT primaries on the EL84 pin sevens which resolved the issue.

I found that all combinations seemed to push the EL 84’s into clipping as suspected but confirmed for my self the distasteful results lol. I abandoned that idea realizing now why very few “mini” amps or 18 watt amps that produce over driven gain have this type of Presence. There is a Randal Smith method but I decided to pass on that option as I had other plans.

Once I abandoned the NFB Presence idea I fine tuned the preamp to my ear. Drilled my holes for the bells and whistles and put everything in place with proper lead dress. I did not use the clippers over my 2 hours of playing while starting the flow/burn in time settling all of the 25+ new components.

By the time I finished the HPT20 was sounding huge. My fiancée was laughing at how huge the tone was coming out of that little mini through my 2 UK V30 Marshall cabs as she has listened to the final production of every single one of the 60+ 50/100 Pandora’s, MorningStars and SoCaliDondo’s I created in 2018.

The owner is especially excited.

I talk in depth with every person I do work for. Many are members here. A couple are return customers requesting 2-3 amps. Back to the point. I had a blast with this little guy and have had a few inquiries to date with one inbound along with more Pandora requests.

I have been accused of “run on posts” lol. Non the less, if you have additional questions that I feel I can answer please ask fusebrain.

Thank you for your interest in this endeavor.

David

 

[Mailman1971]

Fight the good fight David!
Your mod sounded great

 

[NewReligion]

Fight the good fight David!
Your mod sounded great

Thank you. I "Never Surrender".

David...♫