What's the best place to elevate heaters?

[frank57]

I tried this test on the second filter cap but there was no improvement with buzz hum.
Better to try off first filter cap or elsewhere?
I assume it's working?
There was a bit of a voltage drop from 376 to 368 and the bias went a little lower too.
On this Hiwatt I get on 4 and 5 on the el 84: 65v dc.
On the preamp tubes I get 65.3 dc on 4,5 and 9.
Also on 9, I seem to get some ac voltage as well, 3.68.
9 to 4/5 is 6.38 ac I think.

An artificial ct seems to help some so I'll try that hooked up to this board.
If elevating heaters is a dud does that mean dc power would do very little as well?

[jojokeo]

You should always form an artificial CT and then attach that to your raised voltage. I would lower the voltage also to between 35v and 40v. going any higher isn't necessary. Also, this isn't the "cure-all" to noise problems. Noise floor is all about component mounting, layout, lead dress, and grounding. With that flat single plane circuit board there are already inherent issues that which can't be avoided.

[tubeswell]

If it hums the same with or without heater elevation, then the hum is coming from something else.

[stingray_65]

Re: What's the best place to elevate heaters?

In a breezy bungalow overlooking a Hawaiian beach,

but that's just my opinion, take it or leave it   

[Willabe]

Re: What's the best place to elevate heaters?

In a breezy bungalow overlooking a Hawaiian beach,

         



           Brad

[jojokeo]

Ray, sure you don't mean "hooters"?

[HotBluePlates]

Did you ever say you cut the heater traces on this amp and simply ran 2 wires? I can't remember all the threads on this amp.

I think you'd said you reduced the buzz when you used a battery for the heaters. A.C. heat should be good enough to be quiet, so the next best option is run a twisted pair to the heater pins and cut the board traces to the heater pins.

Or not. But you've probably tried everything else.

[Colas LeGrippa]

the first goal in elevating heaters is to respect the cathode/heaters max voltage in order to preserve the tube's life
noise mainly comes from gnd loops and signal wires not shielded. As long as the signal is carried by the high voltage, ( before the coupling cap), no problem, but just as past the cap, use a shielded wire to the grid of the next tube, shield grounded one end only to avoid gnd loop

regards

[frank57]

No I never cut the actual heater traces themselves.
Twisting the heater wires didn't do much.
But maybe the wires from the OT might be contributing?
You mean cut them and twist the wires and so on?

Elevating the heaters with the artificial ct seems to help more with the hum from the mv.
Or it's mainly the artificial ct doing the work.
No effect on the preamp buzz at all.


The signal wires on the grids of v1 and v2 are shielded.So is the plate on v1.
The amp was made that way.It helps but they didn't use a shield on pin 6 of v2b.
The outside possiblity is the lack of a hiwatt tonestack might be contributing to the problem.
Maybe those filters in there might help.

It seems to be mainly a preamp problem.
Buzz from the treble and hum from the middle, gets worse with the gain is used.
The gain itself with treble and mid off and bass on does not generate buzz.

What's worked is:

1)An artificial ct helps reduce hum from the master,but adds some hiss.
The original ct looks like is a little hummy.
2) taking out a gain stage(v2b and eliminating the efx loop)pretty much cleans it up
but toughh to play lead on.(some sound samples here:
http://www.mediafire.com/?x2m8o33s3af31ra
http://www.mediafire.com/?0f4ela4im33a6eb
3)reducing r8(to 47k) or reducing the mid pot.
4)battery test worked but tubes didn't light up.
5) moving the hv wires away to the sideboard reduced some of the hum from Master.
6)reducing the 470pf treble cap to 220pf.
7)anything that reduces the middle stage.
Reduce plate to 100k.
Increase the cathode to 10k.
8)Rejigging the ground plane helped a little with hum
9)Increasing filter caps here and there helps a little with hum.
10)removing the original ground loop in the amp helped reduced hum.
Grounding the input jack in the bolt hole near the front did nothing.

Is there any other place I can move the hv wire from the ot?
I'm still suspicious of the PT.Turning it affects the buzz but doesn't eliminate it.
Is a 2 side board a better way to design this type of amp?
I'm thinking to go back to the low gain version which is very very Hiwatt like.
Power tube distortion all the way but it needs more gain somehow.

[jojokeo]

Without going into all of your details, you're seeing what troubles can happen when the amp manufacturer/designer has taken many considerations into account for production, costs, simplicity, etc...it's all about compromises being made. You're HEARING the results.
Components' placements, layout, lead dress, grounding, etc. are all issues you're dealing with as I mentioned earlier. You can try as you might, but you're going to end up not satisfied and spending time and money but still not getting to the root of your problems...unless you do things completely over. You don't know and realize what all of these are. But again... time and money on this amp...is it worth it to you? Are you willing to make a new board, is there room, do you have the time and money, do you know how and what to do, etc. ??? At some point it's time to fish or cut bait or put up with it. The frustration also may not be worth it. - just my 2¢

[frank57]

I was thinking of gutting it and trying to get the Hiwatt dr210 in there.
I can't quite figure out what the r12 resistor is on that thing.
http://www.el34world.com/Forum/index.php?topic=12382.msg115141;topicseen#msg115141
It will fit I think but there would be quite a bit of work to do.

For now I might use it as is until something better comes along.
Maybe take the stupid efx loop out again.It's just adding noise.
It's a shame because the transformers are huge on this thing.
It's tough because I wasted so much time on it and so on, but one way out is to go low gain or disconnect the efx loop .That makes the amp useable up to noon.

This particular Korean Hiwatt amp is very similar to the Hiwatt lead 20.
I traced out the preamp and it's a hiwatt all the way.
The back power section looks similar to the l korean one,
with maybe the efx loop running off the tube stage.
http://s871.photobucket.com/albums/ab274/sextonpm/Hiwatt%20Lead%2020/
That was another pcb based amp but much better layout.
The power section is almost identical.So for el84 based Hiwatt that would seem to be the way to go.
They're all variations on the Hiwatt overdrive lead.

[kagliostro]

I was thinking that you spent a great amount of time to try to fix that amp

May be you can solve the problem in a way that may seem very laborious but in the end in a relatively short time, compared to all the time used up to now

Rebuild the amp with a new turret layout, not PCB

Kagliostro

[Colas LeGrippa]

yeah, from the very top, point to point.

good........point, kagli.

[frank57]

I'm thinking to do that too, but it's a bit tricky.
The tubes are way too close so how would I get around that?
I would have to get kevin Oconnor's book and figure out how to lay
it out properly.
But what would I try to build, what's in there or the Hiwatt sa210?
How tough would it be for someone who knows how to do it?

[kagliostro]

Here you can find lot of documentation about original Hiwatt (layout & DIY indications)

http://hiwatt.org/tech2.html

about the fact that tubes are so close, have you considered shielding the preamp tubes ?

Kagliostro

[frank57]

You mean with the shield can type things?
Those are there. They do nothing unfortunately.
I'm going to try a hunch with the treble pot and see if the buzz goes down with something resembling a hiwatt tone stack there.The resistor at r8 is 470k in this amp on the hiwatt ol it's either a pot(470k) or a resistor at 47 or 56k.
I'm trying to figure out the hiwatt dr210 or sa210 too.
More of a marshall I think than a hiwatt buy hey it might be pretty good.
http://www.el34world.com/Forum/index.php?topic=12382.0

[frank57]

Okay this is cutting the buzz way down.
http://www.el34world.com/Forum/index.php?topic=12621.0
Now why is that?
Is the lack of a Hiwatt tone stack part of the problem on this amp?