New to forum looking to rebuild Dynaco Mk 2s and a 3

First pass at new Caps
I ran out of time last night and didn't get to take pictures with good lighting - I will replace these next week when I return to that house (I am off to my cabin for a few days - will return to that house Tuesday or Wednesday).

Mk2-#2
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Mk2-#1


Basically, I replaced the Caps in the Quad can with new caps.
-  For the 30uf/500v I used two 100uf/400v (wired as 50uf/800v).
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-  For the other three I used two 56uf/400v (wired as 28uf/800v). It is hard to se in these pictures but I placed stacked Caps dead center wired them to eyelets 5 & 6 on the circuit board. I wired in a resistor to 5 running back to the connection near the Quad Cap. I ran a new ground for these Caps to the main ground strip (I had to run similar grounds back to the ground strip on one amp for the Cap I placed where the Quad can connects to the chassis).
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-  I used a 100uf/400v Cap for the Bias Pot and a 100uf/100v one at the diode replacing the existing previously incorrectly installed 47uf/100v.
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Next step is to trace out everything and make sure I didn't make any mistakes.

MrBlimp wrote: First pass at new Caps
I ran out of time last night and didn't get to take pictures with good lighting - I will replace these next week when I return to that house (I am off to my cabin for a few days - will return to that house Tuesday or Wednesday).

Mk2-#2
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Mk2-#1


Basically, I replaced the Caps in the Quad can with new caps.
-  For the 30uf/500v I used two 100uf/400v (wired as 50uf/800v).
" />

-  For the other three I used two 56uf/400v (wired as 28uf/800v). It is hard to se in these pictures but I placed stacked Caps dead center wired them to eyelets 5 & 6 on the circuit board. I wired in a resistor to 5 running back to the connection near the Quad Cap. I ran a new ground for these Caps to the main ground strip (I had to run similar grounds back to the ground strip on one amp for the Cap I placed where the Quad can connects to the chassis).
" />

-  I used a 100uf/400v Cap for the Bias Pot and a 100uf/100v one at the diode replacing the existing previously incorrectly installed 47uf/100v.
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Next step is to trace out everything and make sure I didn't make any mistakes.

I think you just made a mistake.
Get the real can caps ( from dynakitparts) and save yourself a can of worms with odd caps,
hanging free , hot and missing voltage equiilbration(have you thought of that ?)
Spend your time and effort on new tubes and maybe new circuit boards.

I think you just made a mistake.
Get the real can caps ( from dynakitparts) and save yourself a can of worms with odd caps,
hanging free , hot and missing voltage equiilbration(have you thought of that ?)
Spend your time and effort on new tubes and maybe new circuit boards.

I am not so sure of this. Quite often I will restuff a can. Equally often, I will mount single caps underneath and/or outboard, leaving the (disconnected) can for appearance. On very rare occasions, I will build a small cap-board if I have the room to mount where most convenient.

What I will not do, is create any of the offenses you enumerate. With a houseful of cats/dogs/wives/grandkids/miscellaneous hangers-on, I am kinda-sorta belt-suspenders-Velcro when it comes to general safety.

Some additional facts:

Parts-&-Pieces mounted below the chassis are necessarily cooler than those mounted above. Note that the OP is using a mix of 95 C. (203 F.) and 105 C. (221 F.) caps.

Correct use of soldering techniques, heat-shrink insulation, mounting techniques and so forth, are, in fact, much more reliable means of preventing a hot chassis or stray voltages than a can-cap, which, if it fails-short puts up to 500 VDC right onto the chassis.

Caps mounted in series can greatly increase operating voltages, and taking advantage of smaller caps these days, one may also increase capacitance at the same time. Adding small snubbers is also easier.

Point being that the option noted may be executed with equal-or-better safety, equal-or-better results and at a significantly lower cost - which will make new/better boards a more likely option.

.

There is a difference for an experienced engineer to change a circuit or modify a device while at
the same time have all security and reliability issues fully in mind.
In this case , replacing a can cap ( where there exist perfect spare parts) with a loose gathering of
axial capacitors, supposed to be held in place by something and at the same time make sure
that none of them will exceed it's design parameters.

If i am perceived as offensive, i apologies. That is not my intention. But i usually speak what i mean
and if someone asks for advise i will say my opinion.

The opinion is : don't build a birds nest of loose caps in an amp. Use proper spareparts and feel
confident that it will work and not be less safe then the designer intended.

peterh wrote:There is a difference for an experienced engineer to change a circuit or modify a device while at
the same time have all security and reliability issues fully  in mind.
In this case , replacing a can cap ( where there exist perfect spare parts) with a loose gathering of
axial capacitors, supposed to be held in place by something and at the same time make sure
that none of them will exceed it's design parameters.

If i am perceived as offensive, i apologies.   That is not my intention. But i usually speak what i mean
and if someone asks for advise i will say my opinion.

Not hardly offensive - and not taken that way even a little bit.

I am suggesting that there are usually several solutions to any given challenge of this nature. And on an historical note, David Hafler used can-caps to:
a) Preserve real-estate.
b) Because they were MUCH cheaper (back in the day) than separate caps.
c) Emphatically NOT because they were more reliable - although give him some credit for picking a reliable source of the day.

Peter W. wrote:
Correct use of soldering techniques, heat-shrink insulation, mounting techniques and so forth, are, in fact, much more reliable means of preventing a hot chassis or stray voltages than a can-cap, which, if it fails-short puts up to 500 VDC right onto the chassis.

Caps mounted in series can greatly increase operating voltages, and taking advantage of smaller caps these days, one may also increase capacitance at the same time. Adding small snubbers is also easier.

Point being that the option noted may be executed with equal-or-better safety, equal-or-better results and at a significantly lower cost - which will make new/better boards a more likely option.

I certainly used a good deal of heat shrink insulation where ever possible.

PeterCapo wrote:Given MrBlimp's unfamiliarity with these amplifiers and his starting out on a learning curve at Post n°1, I think it would be prudent to opt for a more basic and more readily verifiable route.  I'd get a refund for all those parts and get the quad cans - less chance of going Hindenburg with this project.

Though my current experience is low I do have years of previous experience. Plus my dad was a electronic technician who dealt with transistors, resistors, capacitors, etc... from back when he was one of the first nine men who certified to work on the new technology called radar to his death. And, before I turn this thing on I will be meeting with my cousin to walk through my choices. He spent 40 years on the LIRR crew repairing the circuits for the track switches.

peterh wrote:There is a difference for an experienced engineer to change a circuit or modify a device while at the same time have all security and reliability issues fully  in mind.
In this case , replacing a can cap ( where there exist perfect spare parts) with a loose gathering of
axial capacitors, supposed to be held in place by something and at the same time make sure
that none of them will exceed it's design parameters.

My viewpoint is that the original designer of the circuit may not have been the one to choose the components. Even if they were, the components, as within any company driven by finances and a bottom line, had to be chosen based on best costs. The fact that some Caps were originally lose and some were in a can leads me to believe that the person selecting the components chose the Quad can because it kept all of those Caps in one location which best supported the wired connections and, most probably, was the most cost efficient way of supplying numerous 500v Caps (seems it still is to this day). I personally do not see that 4 Caps in one can are part of a good design. Plus, my design is a tried and true one. I'll admit not by me but I know of at least 3 other people (who do repairs for a living) who have used it and I am sure that in the instrument amplification marketplace many others have done the same - I have been in quite a few amps in my roadie days in which I have seen very similar repairs/modifications.

peterh wrote:If i am perceived as offensive, i apologies.   That is not my intention. But i usually speak what i mean and if someone asks for advise i will say my opinion.

No offense taken. I am a firm believer in people being able to say what they think as it can lead to constructive discussions, which is why it is often called "constructive criticism". What I am not a believer in is insulting and demeaning people, which I see as a demonstration that the person doing so knew they were wrong and decided to lash out in a lame attempt to appear superior.

peterh wrote:The opinion is : don't build a birds nest of loose caps in an amp. Use proper spareparts and feel confident that it will work and not be less safe then the designer intended.

There is something to say for what I have done simulating a "bird's nest" but I still stand by my thoughts on why I chose this method.

Furthermore, this is the power circuit, of which there are a few variations (William's, Mullard to name two that I know of) not the audio circuit, which I would not take suck liberties with.

"Bird's nest" aside, where I could be criticized, at least in my opinion, is in my choices of using higher capacitances and voltages. It is my understanding that in a power circuit going up is always a benefit and going down is not to be done.

Peter W. wrote:
I am suggesting that there are usually several solutions to any given challenge of this nature. And on an historical note, David Hafler used can-caps to:
a) Preserve real-estate.
b) Because they were MUCH cheaper (back in the day) than separate caps.
c) Emphatically NOT because they were more reliable - although give him some credit for picking a reliable source of the day.

I totally agree to item "c)" - Big Time

As for item "a)" it may have been beyond just "real estate" as it could have also affected tooling for creation of the chassis (like an added punched hole to accommodate some other approach or a larger chassis to accommodate room for the extra Caps), which all would have added significant costs.

.

PeterCapo wrote: Given MrBlimp's unfamiliarity with these amplifiers and his starting out on a learning curve at Post n°1, I think it would be prudent to opt for a more basic and more readily verifiable route.  I'd get a refund for all those parts and get the quad cans - less chance of going Hindenburg with this project.

MrBlimp wrote: Though my current experience is low I do have years of previous experience. Plus my dad was a electronic technician who dealt with transistors, resistors, capacitors, etc... from back when he was one of the first nine men who certified to work on the new technology called radar to his death. And, before I turn this thing on I will be meeting with my cousin to walk through my choices. He spent 40 years on the LIRR crew repairing the circuits for the track switches.

PeterCapo wrote: I was referring to your Dynacos, in particular.  Please feel no need to justify yourself.  I was just trying to suggest a way to reduce the likelihood that you will run into complications.  Of course, they are your amplifiers to do with as you please.

I wasn't justifying myself, just explaining that my experiences are larger than may appear from what I posted in this thread.

Like I said in another response, I enjoy constructive criticism and I have paid great attention to everything that has been written in the posts in this thread. It has all been extremely helpful and made me think hard and extensively about things in great detail before making any decisions. Even the stuff that goes against my decisions.

One of the decisions I thought at length about on the Caps was should I go with one Cap (rating matched to the schematic or higher than the schematic), two Caps in series (doubling the VDC but halving the uf), or two Caps in parallel (two with the same rating to add up or one with a larger rating than the other with both being the same material, or one with the larger than the other with the smaller being a different material).

I know they all have different effects, and I know that their filtering can affect things differently, but there are other things to look at. Besides, it seems a standard rule is higher ratings are never bad, but lower ratings are, so I decided on the two in series for most all of the Caps that had been in the Quad can giving me higher VDC ratings but only half the uf ratings which was still slightly higher than the original uf ratings, and one with higher ratings for Caps in the Bias circuit (this was where my amp had lower ratings than what was on the schematic).

We would probably also have to add into this discussion a consideration of the ESL and ESR of electrolytic verses a Cap made with some other materials, and their affect on the circuit and condition of the supplied power, which would be beyond my knowledge right now. Though I do know that the standard electrolytic Caps have a much dirtier supplied power than ceramic caps would. I guess all things being what they are the designers either didn't care or the costs didn't allow for this type of consideration dictating what Caps to use. maybe history had something to do wit it.

Added to all of that, as I stated in a previous post, I will be running my decisions by my cousin before I even consider powering anything up, which I still haven't figured out how to do yet as I haven't gotten into the back of the garage to check if I still have that variac (adjustable power) device (I am quite sure my cousin has one).

UPDATE

I just returned from my cousin's house. He reviewed everything I did and highly approved.

I just replaced the on/off switches in both amps.

Next will be to do something about the 3 caps on the circuit boards of each amp before powering them up.

I plan to bring the amps to my cousin's and use his bench instead of digging my variac out of the back of the garage. He will also visually review my work to double check everything. It is interesting to see someone like him, who hasn't worked on electronic circuits since his early retirement some 30 odd years ago look at a schematic he has never seen before and instantly know everything there was to know about it. Plus he pulled out tube manuals, etc... and reviewed all the connections to the tubes so he was dead on with anything before he spoke.

Unless I have some free time next week, which I don't think I will, I am pretty sure that anything further I do on the two Dynaco amps will be post new year. Probably the second week of January.

In the meantime I downloaded all the documentation I could find for the Scott 121-c preamps and will start studying what I need to do to them. My cousin said I should replace every single capacitor in both units. So the project moves on.

I also downloaded schematics for the Scott 299 and Fischer X-100 integrated amps I own as I expect to bring them back to usability status as my next projects.

..........................It's looking like it will be a fruitful 2019.

 12/19/2018 - UPDATE

Earlier this evening I installed some capacitors on my circuit boards.

The Orange Drops are NEW .22µF / 600v (they call for .25µF, which, other then some supposedly NOS ones on eBay, I haven't located).
The Brown Drops are OLDER/TESTED .1µF / 400v that my cousin gave me.

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I also soldered in Inrush Current Limiters.

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Next step
 Take them to my cousins, review everything I did, check the circuits, test the tubes I have, and power them up on his Variac.

After that I need to start on the Scott 121-c Pre-Amps. I see at least 2 Capacitors that absolutely have to be replaced. There are like 25 other single Caps and a few Multi-Capacitor Cans as well (all of which have to be checked out before I power them up). I've been going through my papers pulling together schematics, etc... I also found some related free downloads on the internet, which weren't complete, so I bought a full Photofact Folder on eBay.

Then comes speakers and turntable. I want to get a set of speakers and a turntable for each system (this one, and the Scott and Fisher Integrated Amplifiers once I recondition them).

For now I'll use a Benjamin Miracord (ELAC) turntable (the model 2220 below it in the picture is a Marantz Receiver that I haven't used in years), and a pair of JBL L88 speakers, all of which my wife and I used back when we lived in an apartment (38 years ago); and then in my daughter's bedroom after she oved out.

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I have to pull the screens on these and check the condition of the woofers, midranges, and tweeters themselves.

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I haven't posted in a while . . . I've had a few neurological issues, which I am just over. In the meantime I was "occasionally" working on my amps.

My older MkII is up and running. I am using a Dynaco PAT-4 (transistor) preamp for now until I rebuild my Scott (tube) preamps (see picture below).

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Those are the original tubes - I bought a new set but am waiting until I finish the other amp before I use them.

For right now I am running it without the cage (I stuck it under the couch for safe keeping. I'll eventually put it on. I just have to remember where I stored the screws.)

The newer MkII had an issue - I had soldered in a capacitor in the wrong direction and it almost blew when we brought it up with the variac on the bench. A week later I correctly replaced the capacitor but when we again brought it up on the bench we found that there was some other issues. One of the transformer leads to one of the EL tubes snapped off. Plus the cuircuitboard had always seemed sketchy. There had already been some repairs to it, and I had tried to repair a few of the tracings. There is also a resistor missing and another soldered in underneath the board in a strange location. So, I decided its time had come and gone and I bought a used matching one on eBay. I soldered it all in this morning. I still have to get to my cousin's to bench test it before hooking it up and pushing some music through it. I thought I could tonight but he was busy. I have to get back to the house my wife lives in so it will be another week before I can possibly bench test it.

Basically I am running the stereo preamp into a Y-cable turning the signal into a mono one and from there it goes into the amp. Out of the amp I am running two speakers, one on each side of the room. Pseudo (mono) stereo.

I decided not to use the  Benjamin Miracord (ELAC) turntable for now and am using a cheap XION Profile Pro one I own - at least until I get everything else up and ready. For speakers I am using a set of HH Scott S-11s that I picked up cheap a few months ago.

So far I've listened to a few albums through it:
1. Flo & Eddie "Illegal, Immoral and Fattening"
2. The Beatles "Let It Be"
3. Leon Russell & Marc Benno Asylum Choir "Look Inside"
4. Steve Miller Band "Rock Love"

The only problem is that one of my neurological issues left me with a strange change to my hearing - many sounds now are heightened and have an almost listening through wax paper sound to them. Plus I have ringing in my ears all day and night long now. It was worse a month ago and it is getting better. I expect by the time I have everything up and working properly my hearing will be back to normal. At least that's my hope.

Ok, that's my update.

I'm very happy with the results so far and enjoying the glow.

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After listening to the one amp last night I decided not to wait until the next time I would be in this house . . . . so today instead of taking a lunch break I took an amp break. Drove to my cousin's and brought the amp up on the bench with the variac. We placed a load on it. We hooked a scope to it to check the wave form. NOTHING.  

So we sat there and scratched our heads.

We decided to start troubleshooting by tracing the voltage end of the circuit and were able to find 500V everywhere it should be. The idea was to try to eliminate things to check on.

So we sat there and scratched our heads some more.

Then my cousin noticed we never hooked a signal to it.

Once we hooked a signal a real clean sine wave appeared on the scope.

I took it home and connected it up.

 Now I have stereo from two pre 1960 amps that I haven't had working since 1978.  

If anyone is interested, here is where I think the problems were:

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Looks like a resistor is missing [ Red arrow - Green arrows indicate where I removed the Orange and Brown Drop caps that I reused on the replacement board] (it appears someone inserted it underneath the board - see both images below), though the one under the board is in a different part of the circuit bridging a resistor on the top side of the board - makes me wonder how this amp ever worked when I used it back between 72 and 78.

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In general the board's tracings were a mess (see Green arrows in photo below). I tried to fix them . . . but decided to just change the board. I found two on eBay. I had to clean them up and as I stated in the previous post I swapped the caps with my new Orange and Brown drops.

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Why don't you get 2 new populated boards from dynakitparts and forget the old buggy ones ?
https://www.dynakitparts.com/shop/pc-1-mkiii-mf-resistors/

peterh wrote:Why don't you get 2 new populated boards from dynakitparts and forget the old buggy ones ?
https://www.dynakitparts.com/shop/pc-1-mkiii-mf-resistors/

I considered this option. The problem is that one of my amps is very old and has the larger circuit board (see the bottom board in the picture below). It also happens that the larger board is the one that was in fully functional condition.

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I toyed around with how I could best fill the space (there's a post on it in this thread).

My first objective was to get them both up and running and to do so as close to original as possible. If some day I decide to upgrade them I'll go with the new boards.

My only real changes involved Capacitors.

I stayed on target for the circuit board (audio circuit) and kept my changes to the power circuit. Basically I doubled the capacitors from the quad cap can increasing their voltage coverage but kept extremely close to their capacitance.