Output Transformer VDC Low

[bkvance]

Neil,
I got 360vac between the center tap and each red wire, will drill and relocate as you suggest. Now what?

[neikeel]

Neil,
I got 360vac between the center tap and each red wire, will drill and relocate as you suggest. Now what?

Good, your PT is probably ok, now with the rectifier out measure the voltage on pins 4 and 6 *should be the same). Then install the rectifier and re-measure, then measure dcv to ground from pin 8

[bkvance]

WOW
update since last:

I found I had blown the HT fuse, so now voltages are good.
One nasty squeal/hum so I checked with Brian Wallace and I have PT wired correctly (thanks Brian)
I lifted the NFB resistor and it went away, so now where do I head to correct this??

[neikeel]

You have the primary wires from the OT the wrong way round. The wires that go to pin 3 of V4 and V5 need swapping over, then put the NFB resistor back and you are good to go

[bkvance]

I will do that and let you know what I have.

Thanks so much,

Cheers

[bkvance]

Did swap now i have the hum from HELL I guess you would call it motor boating???

[bkvance]

one of the KT66 is red plating

[neikeel]

Tried to look at your pics but photobucket is down

Do you have 5k6 grid stoppers on pin 5 of your output tubes and which KT66 are you using?

If you were confident about your initial wiring but you got a vicious squeal (positive feedback) that was abolished by lifting one limb of the NFB resistor then that is classical switched primary wires. Some amps squeal others motorboat when this happens

Presume that you have a Marstran-103 OT with the brown wire as centre tap and the black should normally go to pin 3 V5 and the red to pin3 of V6?

Check simple things like ground connections of your output tubes, that the output jacks are grounded to one of the output tube grounds too and that your bias circuit is also grounded.

Lots of simple things to check before you get too frustrated

[bkvance]

Ok Neil,

Here's where I am :

5.6k grid stoppers are installed at pins 5 on V4 and V5

I did have the Red and Black installed at pins 3 of V4 and V5 and had to change them vs what is documented for the 103 because when I had them like the schematic said I had the squeal from Hell. ( No Squeal now )

I somehow didn't have the output jacks grounded, but they are now.

I replaced the OT Tubes as one of the KT66's was red plating and it didn't matter in which socket I placed it in.


So now I have a quiet amp that is really loud


Thanks so very much for your help

Cheers
Keith

[neikeel]

Ok Neil,

Here's where I am :

5.6k grid stoppers are installed at pins 5 on V4 and V5

I did have the Red and Black installed at pins 3 of V4 and V5 and had to change them vs what is documented for the 103 because when I had them like the schematic said I had the squeal from Hell. ( No Squeal now )

I somehow didn't have the output jacks grounded, but they are now.

I replaced the OT Tubes as one of the KT66's was red plating and it didn't matter in which socket I placed it in.


So now I have a quiet amp that is really loud


Thanks so very much for your help

Cheers
Keith

Phew!

[bkvance]

Thanks again Neil,

Wow this thing is incredible

[bkvance]

Neil,

Is the Bass normally this strong in the AMP?

[neikeel]

Neil,

Is the Bass normally this strong in the AMP?

You mean flubby!
Yes.
For lead guitar work try, presence 8, Bass 0, Mids 8, Treble 8, Vol 1 8 and unused ch 2 4 (it interacts)

That is your starting point. Use your guitar to go from clean to dirty. (You need good guitar controls!).

[bkvance]

Cool

Thanks again Neil