Opinions on my heater wiring work

[FunkyE9th]

Assuming all the proper grounding and signal routing has already been done, you should be able further reduce the heater hum by increasing the bypass cap on the 1st stage (22 or 25uF). It will change the sound, but you can compensate by changing the coupling cap to a smaller value.

[Bill Moore]

I certainly not the tech that most of the posters here are, but I built my last (AB763 Twin) build with the heater wiring close to the chassis with loops between tubes. I tried this because I had a '94 twin chassis that Fender wired like that. It is fairly quiet, and think I will try it with my next (AB763 Deluxe) build. I did of course run my signal wires above the sockets.

[keewee]

I read early in your post about trying a hummdinger, if you are sure its a humm (60Hz) and not a buzz (120Hz) or hiss (white noise) then: 1) try inserting the 6v battery to the preamp tube(s) disconnecting the ac source. If this quiets the humm by all means use the hummdinger, merlins - valve wizard site has a good schematic and explanation, chances are you will only need a small potentiometer - cheap and easy and really works good. 2) If you want to go the DC route check out blue guitar.org There is a schematic for converting your 6.3 ac to dc using a bridge rect., cap and resistors, more expensive but works well too. 3) Above all check out your guitar wiring (swap guitars an cables) flourecent lights, light dimmer switches and computers and montitors all can make humm.
HAPPY HUMM HUNTING

[soma_hero]

Xtian,

It's simple enough to not need a schematic for a DC heater supply.

For a push pull amp: I only wire the preamp with DC. The push pull nature of the power section cancels out most of the hum that may be introduced from AC heaters. If your heater secondary has a center tap, then ground it and run AC heaters to your power tubes. Then run the heaters to a Full Wave Rectifier. So just each wire from the heater secondary goes to a rectifier diode anode, the cathodes of the two diodes are connected together. Now you need to adequately smooth the DC so put a big ol filter cap on it. I've used 15,000uF with good results. One amp needed 22,000uF.

If you don't have a center tap, just run AC to the power tube heaters and then use a bridge rectifier and the smoothing cap. This may end up being higher than 6.3V in which case you can use a dropping resistor to lower the voltage. This will also help keep the voltage a little more regulated.

For single ended amps like you've said you've done, you should probably run the whole amp on DC heaters.

[surfsup]

I hope to find a 6v battery somewhere soon to try running the heaters off that instead. I have a bit more info:
--------------------------------------------------------------------------------
I tested all the solder resistance with my DMM. They are all good.

I then started testing the resistors by clipping the alligators to the lead of the resistor. I did every one in the amp. Here's what's interesting, all the resistors tested fine except the 220k 1watters (there are 5):

[img691]http://chicagocadcam.com/ChrisHahn/HO220s.jpg[/img]

For R1 in parallel with C1 just after the switch, I get R1=25.59k (way less)
For R16/17 I get ~127.8k for both
For R20/21 I get ~113.7k for both

Questions
All the other resistors test out to within a few % of their actual values. Is this right? Could this be a source of the problem?

you should be able further reduce the heater hum by increasing the bypass cap on the 1st stage (22 or 25uF). It will change the sound, but you can compensate by changing the coupling cap to a smaller value.

So you are referring to increasing C16 (bypass cap) but reducing C15 (coupling cap)?

[Structo]

Generally you will have to lift one end of a component to measure it's value.

When in circuit the other components will throw the value off.

So none of those measurements are valid.

Besides they most likely don't have anything to do with your buzz.

I think if you ran your heater wiring correctly, either above the sockets or on the floor but away from the other wires you can tame it.

If you do have to cross another wire do it at a 90 degree angle.

The bypass cap on stage one is the .68uF and is small.
That is a typical Marshall value.

You can try a 4.7-10uF there, a 22uF will increase the bass quite a bit.

How are you running the heaters on the preamp tubes?
I ask because I see you have the wires going to pins 4 & 5 but not to pin 9.

[surfsup]

Generally you will have to lift one end of a component to measure it's value. When in circuit the other components will throw the value off. So none of those measurements are valid.

Okay, I thought maybe I got a bad batch of 220k because all the other resistors tested correctly. For the heaters, you can see here the green supplies pin 4-5 and the yellow for pin 9. On the second preamp tube, the yellow that runs vertically is per the schematic linked in my previous post with 129V across it:

[img1000]http://chicagocadcam.com/ChrisHahn/a1.jpg[/img]

I guess I can try and rerun the heaters to that second tube and not have them go across the socket like they do now. I also plan to put a grid stopper resistor on pin 7 tube 1.

[Firestorm]

I think the R values are what you'd expect in circuit. R1 is paralleled by C1 which will conduct until it charges (which it never will because of R1). R16 and R17 and R20 and R21 are in parallel (when you measure them) so you'd expect to see half the R value. As Structo says, probably not the issue anyway.

I wouldn't be too quick to change the .68 on V4B: a lot of Marshalls do hum with that value, but elevating the heater supply shuts them up pretty effectively.

V3 looks dicey with the heater wires crossing everything as Martin (I think it was) pointed out. When you elevate the heaters on a cathode follower, you actually bring the 60Hz AC closer to the cathode potential.

Doubtful that it matters at the published voltage, but what type of 12AX7 are you using in V3? Some newer ones absolutely detest being run as cathode followers.

[surfsup]

The two preamp tubes are all ECC803S I think from JJ on the box if memory serves.

I plan to redo those heaters maybe tonight. I just worked up a revised schematic of the 100R "humdinger" with the elevation circuit (45.8V if memory serves) as well. The actual circuit is shown in the last photo of my pics at the link:

http://chicagocadcam.com/ChrisHahn/amp.html

[img::]http://chicagocadcam.com/ChrisHahn/PS_HO_elevation.jpg[/img]

[surfsup]

I found this on the forums:

[img:399:213]https://tubeamparchive.com/files/thumbs ... rs_902.jpg[/img]

Looks like I have half this already built. Would it be a waste of time to build this (diodes forward)? Comments on the previous thread were the filtering was not great and to use bigger cap(s).

[Firestorm]

ECC803S is a long plate spiral filament tube. The long plates can make some of them a bit microphonic (but not always). The spiral filaments reduce hum from AC heater supplies. Haven't heard anything bad about these as cathode followers. The spec sheet says 200V cathode to heater (plus you've elevated the heater supply) so should be fine.

[Jana]

I should have written my name on that, i could be famous by now, lol.

[Firestorm]

I should have written my name on that, i could be famous by now, lol.

I thought you were famous ...

[Jana]

I guess I am famous, or at least a legend (in my own mind). The funny thing is, the older I get the better I was!