mark III power transformer hum

i have a pair of mark III's that i've installed vta boards in and both of them now have a power transformer hum. the hum is in the transformer and does not hum through the speakers. it does not increase with volume. i've checked everything and double checked everything. all connections seem good. i've even pulled a tranny from another set of mark III's that does not have any hum at all and it hums with the vta board. i've contacted roy and he can't help at all. i've changed output tubes and rectifiers and still the same hum. everything is grounded as it should be. the quad caps are new but i replaced one just to be sure and the same thing. i'm just about at my ropes end and i'm considering removing the vta boards and getting something else. i remember someone else on this forum having the same problem. does anyone out there have a solution or a suggestion?

hum from a transformer is mechanical movement. usually its when a transformer is being over-loaded but can also be caused by the material the transformer is made from, for lack of a better way to put it, becoming looser. if the transformer get really hot then its a sign of over-loading and you should discontinue use and get a transformer that is rated for the current demand. the original design used 1 small tube (6AN8) and the VTA board uses 2 either 12__7's or 6SN7's. so there is more current draw for the extra filaments. just keep tabs on the transformer temp - if it gets too hot to touch then your transformer needs to be replaced. if not then its just a mechanical issue in the transformer and there is no immediate need to replace it unless the noise is bothersom.

i'm wondering now whether the quad cap is orientated properly. can someone post the proper orientation of the 80 40 30 20 upgrade quad cap with the vta pcb. please use the symbols

the quad caps came from dynakits and their diagram shows the orientation as #1 square, #2 half round, #3 round, and #4 diamond. after looking at another post, roys diagram shows the orientation as #1 half round, #2 square, #3 diamond, and #4 round. which is right?

Hi -- with the Dynakitparts 80-40-30-20 Quad Cap (550/600v) --

Half-Circle (40MF) faces back panel -- attach 1/2 choke and Red Output Tranny Wire.

Square (80MF) faces the GZ34 Tube Socket -- attach other 1/2 choke and the wire from Pin #8 of the GZ34.

Run a Jumper Wire between the Circle (20MF) and the Triangle (30MF).

Attach 6800 Ohm 2 Watt Resistor between the 80MF and 30MF Tabs

Run a Wire from the 30MF Tab to the B+ of the VTA PCB, the 30MF Tab faces the RCA Jack.

I have several pairs of Roy's Mk3 VTA Boards wired this way with the Dynakitparts Quad Cap.

Hope this helps!!

hello stewdan, the quad caps i have from dynakits are as follows: half circle 80 mfd, square 40 mfd, triangle 30 mfd, and round 20 mfd. this is different than your orientation. how should these quad caps be wired?

Hi Again ---- CORRECTION to my Original Answer -- the 40MF faces the GZ34 Socket and the 80MF faces the back panel -- sorry about that!!!

The SQUARE is where the connection to the Rectifier is made.

The HALF-CIRCLE or ROUND is where the connection to the Output Transformer is made.

(I even drew myself a diagram of a working Mark 3 VTA and then proceeded to type the 40 and 80 incorrectly in my first answer to you???)

===>>> Half-Circle **(80MF)** faces back panel -- attach 1/2 choke and Red Output Tranny Wire.

===>>> Square **(40MF)** faces the GZ34 Tube Socket -- attach other 1/2 choke and the wire from Pin #8 of the GZ34.

Run a Jumper Wire between the Circle (20MF) and the Triangle (30MF).

Attach 6800 Ohm 2 Watt Resistor between the 80MF and 30MF Tabs

Run a Wire from the 30MF Tab to the B+ of the VTA PCB, the 30MF Tab faces the RCA Jack.


Is this how you have your Quad wired up??

thanks for the correction. everything is wired correctly. the noise i'm getting is more of a buzzing sound than a hum. everything is tight and everything looks to be wired correctly. i even put additional screws in all of the trannies to hold the plates together tightly. i'm now wondering if it's something with the vta boards. one buzzes louder than the other but they are both discernable from 4 or 5 feet away. very annoying.

Hi Again --

There was Forum Post back in March (I think??), with the title "octal option??".

Take a look at the 2nd page of the Post (actually, Post #24) where Roy posted a wiring diagram (which is also valid for the 12XX7 versions of the VTA Board) and see if your wiring agrees with his.

I am wondering if maybe there is a grounding issue and you are picking up something????

Stew

take another look at that post. the symbol orientation is totally different than what you or i have. that's the post that got me wondering if i had my quad cap misorientated.

Actually, I think the diagram was based upon the Stock Dynaco Quad.

But what I was thinking was one of your Grounding Wires to the VTA Board did not look like Roy's Diagram???!!! Anyway, take a look.

Also, a few years back, there was a Forum Post from DanF where he talked about how he wired his Mark IIIs because of some "noise". If you do a Search by author in the Basket, you will probably pull it up. See if his noise is your noise??

Stew

i discussed danf's fix with roy and he recommended not doing that. he looked at my wiring and could find nothing wrong. said that hums are sometimes hard to fix!! i'm beginning to lean more toware the vta boards having an issue. they were stuffed by roy so i can't verify that they were stuffed properly or not. i'll give the forum a couple of days to possibly shed some light on this issue and if i can't get the problem fixed i'm going to remove the boards and start over.

what pictures of mine are you looking at?

Hi --

I was not looking at any of your pictures.

All I suggested was that you compare your wiring of the VTA boards with Roy's Picture in the Octal Option's Forum Post and see if there was a grounding issue that caused the hum.

i was asking because i posted pics earlier when i had a runaway bias issue. that issue was resolved. also, i've moved some things around since those pics were posted. i don't think it's a grounding issue.