2. amps-preamps
  3. 190559-99185

Modifying a Coincident Dynamo Mk1

Hello all,

Have been modifying my Coincident Dynamo Mk1 for some time and I could use a helping hand from more experienced users.

If I understood correctly, looking at the image attached the 2 Epcos 22uf/500v are the filter caps which come after the rectifier (in my case the 5AR4) and these have to take into the account the rating of the tube and capacitance limit which is 60uf?

If my ramblings prove to be true can this position be improved on with better caps and/or a slightly larger caps?

Looking at the, what I think to be the power supply cap, which is a 470uf/500v, would there be a benefit in putting a larger cap without causing other issues? For instance the Mk2 Dynamo has much bigger caps in that position but I suppose the transformers are different as well. Id be looking to get more bass and mid bass and some readings say this is the place which can yield some results.

I have done several modifications already with mixed results so if anyone is interested I can share the details but Im trying to learn more about the positions and parts and their relative role. Any ideas and suggestions are welcome.

Link to insides below.

Thanks in advance!

https://ibb.co/JqW6JDb

P.S. For some reason the picture did not want to upload via the insert photo, sorry for the link.

neverlast
noromance's avatar
noromance
9,769 posts
 

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.

sns
3,203 posts
 

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.

neverlast OP
15 posts
 

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

 

imhififan's avatar
imhififan
2,181 posts
 

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.

neverlast OP
15 posts
 

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? 

More to discover