New 5F6A Build with Odd Voltages and Loud Buzzing

[MWJB]

Jim911,

You have misunderstood Mandopicker, he was asking about your 6.3VAC centre tap (usually grn/yel - see weber layout), NOT the red/yel B+ centre tap - I can't see a 6.3VAC CT in the picks? What is the orange PT wire that is capped off?

If you don't have a 6.3VAC CT you need to solder 2x100ohm resistors to ground, one resistor goes to one side of the heater winding, one resistor goes to the other side of the heater winding. Most folks install these resistors on the lamp assembly (remove the lamp bracket from the amp & solder the resistors to the bracket itelf, from each lamp terminal, refit the lamp assembly).

How did you solder the wires to the brass plate, you should have soldered the ground wires to the plate before it was installed in the amp, so that the plate gets hot enough to solder to (when installed, the chassis acts like a heat sink making the job harder). Your solder at the ground points don't look smooth & shiny enough?

[mbratch]

That's what I was looking for: the green/yellow 6.3VAC CT wire. The Weber layout shows it grounded, but I don't see i tin the pics.

[Mandopicker]

Without the CT of the filament supply in the power trans, the 2 x 100 ohm resistors will do the trick.

IMO:
It really serves no purpose to track down other noises until this specific area is fixed. Pretty easy to tell if the ransformer has the CT for Filaments (greenw/ yellow stripe) or even if the 2 x 100 ohm resistors for the Artificial CT were used. (Attach one from each lug of the pilot light and ground the other ends together.)

After that, the grounding issues can be looked at knowing that other major areas of concern are under control.

[Bruce / Mission Amps]

His very first picture, if you choose to look at it, has a grounded green wire.
Yet, the 6.3v filament leads look to be brown heading over to the pilot lamp assy.

[Mandopicker]

Good eyes...thanks.

I was curious about those brown wires. I guess I haven't used a trans with those color codes yet.

On that note...I have a transformer with whitish wires that appear to be the 5v winding...have you ever heard of them being white?

[mbratch]

His very first picture, if you choose to look at it, has a grounded green wire.
Yet, the 6.3v filament leads look to be brown heading over to the pilot lamp assy.

I assumed that the green wire in that pic was the ground from the AC cord. The pic isn't wide enough to tell otherwise. And I saw the yellow/red grounded wire. But no 6.3v CT green/yellow from the PT, or virtual CT from the pilot. So I figured he was missing that.

[jim911]

Thanks all for your posts and advice I had a busy day and am just getting back at the project. I had indeed missed the 6.3 volt CT as previous projects had the green/yellow center tap wire and this Heyboer PT doesen't have one. I did install the 2 100 ohm resistors from the two pilot lamp terminals and this took away the very loud buzzing that I was experiencing.

It has however been replaced with a lower volume, low hum ( I assume what I often see reffered to as 60 cycle hum) and very low distorted (almost with a combination of very lite trem/reverb added) guitar volume. So where I had what seemed like almost full volume with abrasive buzz, I now have hum and low distorted volume.

Can this also be caused by a flawed grounding layout?

I did replace the GZ34 rectifier with a 5U4G (thanks for the suggestion MWJB)and that dropped most of my voltages by a good 20 to 25 volts.

I did contact Heyboer and they confirmed that this is a 120 volt PT and that the 6.3 v wires are brown (sort of odd) and that there is no 6.3 v CT. They identified the orange wire I had capped as a shield between the primary and the secondary and that it should be grounded. I took that to the same bolt as the red/yellow wire for the primary CT? Is that o.k.?

I guess the next step is to rework the grounding scheme as close to the Hoffman recommendations as possible, to see if that helps.

Any other thoughts are welcome and once again thanks to all who have provided input.

[MWJB]

Yes, the orange sheild will be fine at the same PT bolt as the red/yel CT.

[jim911]

MWJB thank you for that confirmation on grounding of the orange shield wire.

[Mandopicker]

I guess I should stick to my guns...glad the 2 x 100 ohm resistors CT helped.

Good job!

[jim911]

Mandopicker

Thanks for the heads up on the 2 100 ohm resistors to provide the 6.3 v cenertap I had over looked. That did get me over the hump on the super loud buzz I was experiencing and on to the next stage of apparent grounding issues.

I've been swamped at work so may not get time until this weekend to get much accomplished but will keep at it.

Thanks again

[lmolter]

When I built my Bassman, I had very similar hum problems as you described. Through numerous posts here, and a great grounding diagram I got from el34 (el84? -- my memory is going), I isolated the hum to the fact that I had the bias supply grounded to the same point as the preamp supply. After splitting the grounds up, removing the brass plate, and soldering all the pots' backs together, the hum fell drastically to almost nil. BTW, soldering to non-solderable-back pots is a nightmare. I trashed all the originals and bought solderable ones. And a length of 12GA buss wire to connect them with.

I haven't read all the posts here, but did you remove the preamp tubes and listen for hum? Mine definitely was introduced in the first preamp. Splitting the ground help that.

And why did you swap out the GZ34? When I swapped mine out (for kicks), the voltages went way up. I put it back and never had a problem. Just curious.

Larry

[VMR]

I know this thread is old, but I'm curious if the problems were ever solved. From the pics the first thing I noticed is it doesn't look like the 3rd tab of each volume pot was grounded. That could certainly create problems.

VMR