Modifying a Coincident Dynamo Mk1

Here is what was advertised for Mk2:

Power supply filter capacity has been increased by 70% and capacitor voltage ratings have been doubled for increased reliability.

So anyone has an idea how much I could size up the reservoir cap and still be on the safe side? 

https://ibb.co/R7YJVdg

I can't tell from the picture above whether the two 47uF 400V capacitors are connected in parallel or in series.

I could be wrong, but it looks like the two large 1000uF 315V capacitors are in series with a 100KΩ balancing resistor across them. If so, the voltage would be doubled, but the capacitance would be halved to 500uF, not much more than the MK1.

I hope someone with MK2 can confirm it.

Thanks guys for all the useful insights and navigating the parts! So basically I could increase the reservoir cap by how much and remain on the safe side? I saw on the Mk2 Dynamo that the reservoir caps are two 1000uf/315V and I assume you cannot just slap these units on the Mk1 and get good results, but would putting another same cap in parallel to mine be possible or should I try one bigger cap?

Heres a picture of the Mk2 showing reservoir and smoothing caps.

https://ibb.co/R7YJVdg

Increasing reservoir capacitance may give you the increased bass and mid bass you're looking for. Film bypass caps on electrolytic reservoir caps good for bass articulation. The other mods you've done or contemplating doing don't really change the quantity of bass. 

Something to consider is you can always remove expensive coupling caps when selling or moving on from this amp, use them in another project,  .47 and .22uf are common values. In my current custom build 300b mono SET's I bypassed PS caps with Duelund's silver bypass cap, Duelund CAST tin coated copper coupling caps and Texas Components TX2575 resistors in signal path. This along with top flight tubes made a huge difference in resolving/transparency capabilities. I experimented with the VCaps and Audyn True Copper Max, CAST won out. Jupiters are very nice for coupling caps as well.

Do not increase the capacitance of the smoothing caps immediately after the rectifier. The charging current will damage the rectifier tube. The 470ųF is the reservoir cap.

If I understand their voltage ratings add up and the uF rating in this case is only half of the first caps value, being 11uF correct?

Two identical capacitors connected in series will double the voltage rating and halve the capacitance value.

Two identical capacitors connected in parallel will have the same voltage rating and double the capacitance.

As can be seen from the picture, these two 22uF 500V capacitors are connected in parallel, so the effective capacitance is 22+22=44uF.

@imhififan to the rescue again, thank you!

So Im still trying to understand if/what can be gained from increasing the two Epcos caps? Also can someone please confirm their respective name and role in the amp (some call the input supply, others power supply etc). If I understand their voltage ratings add up and the uF rating in this case is only half of the first caps value, being 11uF correct? This could leave room for a larger rating since the 5AR4 could endure more?

As for the other single large cap, 470uF 500V, what is its role, what can it improve and is this the reservoir cap (any other names for it?) that @noromance suggested could be doubled if it does not impact the choke rating? 

Thanks for your patience guys.

https://ibb.co/dBt4DhT

Perfect. Nice work.

I tried embedding the image source but there is something up with the site coding.

@noromance, I wanted to post the original photo of the amp for starters to see where people would suggest their own ideas for modding and maybe being a little easier to navigate, also my version does not show the values on the stock power supply cap. But if it may be of any interest to others here is the current state of the amp.

https://ibb.co/dBt4DhT

For some reason Im still having issues with the image showing in the post thus the link.

@neverlast Why didn't you post a photo of the current amp instead of the unmodded version?

What I did do was use a pair of Mundor Supreme caps [etc.]

Paul, thanks for joining the topic, and yes I completely agree. After trying several different caps at various price ranges my conclusion was that it is a matter of taste and one has to judge by himself. It also helps to try and forget the "bigger is better" and "cheaper must be inferior" logic and just listen. That being said, the products  have to meet a certain price point and at the end of the day it has to be a compromise to an extent so this synergy needs to make financial sense. This is where our modding comes in where we try to improve our gear and tune it to our taste.

Israel commented that he does not recommend any other mods other than the ones that were already done, and as I said I understand his point.

Just my opinion, but Israel Blume tried dozens of Caps and values prior to deciding on the best match.

I have modified a few power amplifiers, with assistance from Robert Hovland.  Bob had an excellent comment that has stayed with me to this day.  He said that it is almost never the best Capacitor, Resistor, wiring Etc. that produces the best sound, rather it is the synergy between the circuit and components that usually will sound best. 

Of course, asking Israel, may be a good way to go.

The easiest way to bypass the volume pot is to move the two yellow wires from the center lug to the lugs for the blue and brown wires respectively.

It will eliminate any noise caused by dirt buildup on the wiper.

Removing the pot was my idea when I got the amp but at the time when I asked Israel he told me to just use the pot wide open. Although I sometimes adjust the pot to a lower setting its open or almost open most of the time as I use a preamp.

If you could show an example of how this could be done I would be very interested to try it.

No experience with Audio Note basic pot, TKD is good but expensive. If you are not using the volume control and always set it to maximum, my suggestion is to use a resistor to ground instead of the volume control potentiometer.

Regarding the volume control, I had the chance to hear it can have a dramatic effect in the amp. I have read about these attenuators and they get good reviews the only problem is they are either very expensive or too large to fit, or both. Does anyone have any experience with the Audio Note basic 100k pot or TKD pots?

I would leave the rectifier caps alone.

+1.

To improve sound quality, my suggestion is change the volume control pot to a stepped attenuator like a Gold point, Khozmo or even a Eizz from Aliexpress.

@noromance, thanks for the suggestions! At the time being I have the power supply cap bypassed with a polypropylene Solen 4,7uF and small 0,1uf PPE Solen on top of it. This was a good change but it does not increase the reservoir by much.  After reaching out to Israel on the matter his reply was that he does not recommend any other modifications and I have the feeling that he does not want to get into it, which is understandable. Heard excellent things on the VCap but the prices are a bit too dear for my current budget and also taking into account the value of the amp being modified. What I did do was use a pair of Mundor Supreme caps instead of the Solens with great results.

I do not have a Coincident amp but have worked on other tube amps. I would leave the rectifier caps alone. You could double the reservoir cap by adding another in parallel. Check with Israel to make sure it won’t impact the choke rating (unlikely). I would add a bypass VCap of 0.1ųF/630vdc. Also replace the green Solen coupling caps with VCaps. There are a few other electrolytic caps that could be changed to good quality film like Clarity Caps. Note that film caps need 20+ hours to lose the slight plastic coloration. Check size and clearance before ordering. Do it in stages.

@imhififan, thanks for making the magic happen!

@sns, thanks for the comments, so far I have done the same, just better quality parts (not always better sounding at the end). I will also try contacting Israel on this matter and see how it goes. 

Link to insides below.

https://ibb.co/JqW6JDb

I've done parts substitution on equipment for a long time, generally don't mess with values, these values designed to meet circuit criteria. I generally stick to changing out with higher quality, closer tolerance, same value caps, resistors the same. Higher voltage caps than stock generally ok. As for Coincident products, having Israel change out volume transformers, installing Amtrans selector, changing out PS caps on my Statement pre was nice upgrade. I diy changed out a few caps in signal path. On my Turbo 845SE haven't changed a thing.

Transformers and power supplies critical in tube equipment, I'd contact Israel and ask about possibility of mods you're contemplating. Israel has been fine with me working on my Coincident, I simply related my longtime experience with soldering and changing out parts.