Pair of Dynaco Mark IV buzz. SOLVED

[Fasturd]

Congratulation. What happened was that the filament "drifted" in DC , probably due to small polarity sensitive
rectification in the filment/cathode space.

I hope to know exactly what you said in less than 2 years! LOL!!!

 

[Lavane]

Ya, if your heater winding has a center tap wire it should at leased be connected connected directly to ground. Some heater windings don't have a center tap, so a pair of 100ohm or so resistors should to be added to each of the two leads to ground. I have run into tube guitar amps with no center tap and not terminated to ground through resistors, but doing so makes them quieter.

 

[gadget73]

would be interesting to see what it does with a cap in place of the direct connection, like Dynaco did on other models. My Bogen MO-100a is done that way and those things are flat silent with a driver setup that is essentially the same as the Mark III or IV.

 

[Fasturd]

would be interesting to see what it does with a cap in place of the direct connection, like Dynaco did on other models. My Bogen MO-100a is done that way and those things are flat silent with a driver setup that is essentially the same as the Mark III or IV.

I like the idea of more "quiet" because black backgrounds are great but I am not at the level where I could determine what spec the cap would need to be.

 

[Fasturd]

would be interesting to see what it does with a cap in place of the direct connection, like Dynaco did on other models. My Bogen MO-100a is done that way and those things are flat silent with a driver setup that is essentially the same as the Mark III or IV.

I will take a look at one of my St70s so I get a better understanding of the application.

 

[Fasturd]

Both of the MK IVs are up and running.
Using a virgin PAS 3 and a set of 3 way Peerless Copenhagen teak speakers. And I know it may be sacrilege but I am currently running some of my favorite Jazz CDs through the combination, PERFECT Friday evening…

 

[rustnrot]

What speakers are those? They look similar to some old Argos I have.

 

[Fasturd]

What speakers are those? They look similar to some old Argos I have.

They are Royal Copenhagen 3 way by Peerless in teak cabinets.

 

[TriodeLuvr]

I will take a look at one of my St70s so I get a better understanding of the application.

If the system is quiet by ear now, improvement will require test equipment. You'll need a sensitive AC millivolt meter or preferably a scope. It might also be necessary to temporarily disable the feedback loop for easier noise measurements, because feedback pushes the noise down. In any event, elevating the filament winding is the most robust means of H-K noise reduction. Good luck with everything!

Jack

 

[Fasturd]

If the system is quiet by ear now, improvement will require test equipment. You'll need a sensitive AC millivolt meter or preferably a scope. It might also be necessary to temporarily disable the feedback loop for easier noise measurements, because feedback pushes the noise down. In any event, elevating the filament winding is the most robust means of H-K noise reduction. Good luck with everything!

Jack

I hope to find a "guy" someday that can go the steps beyond as far as scoping etc. however these are doing well at the moment. If I notice more noise when I get them on my JBL C-37s then I may go deeper. I have a few more amps to get safely up and running before I go down the fully optimized road. Thanks for all the advice.