SSS a Hartman Manning Affair

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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning » Wed Jan 10, 2018 5:26 am

So you have a 1R to sense current on each power tube? That should be fine. Does the idle current on the two sides match reasonably well? How about the DC bias voltages at the CF cathodes? Are they close?

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Re: SSS a Hartman Manning Affair

Post by dreric » Wed Jan 10, 2018 5:51 am

martin manning wrote:
Wed Jan 10, 2018 5:26 am
So you have a 1R to sense current on each power tube? That should be fine. Does the idle current on the two sides match reasonably well? How about the DC bias voltages at the CF cathodes? Are they close?
No just the wire from pin 8 to the ground banana jack / 1 ohm 5 watt.
Eric
1949 Zenith, Zenith Toggle Recoil, Zenith 55 & 440

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Re: SSS a Hartman Manning Affair

Post by martin manning » Wed Jan 10, 2018 6:25 am

Ok, I think I see what you have now. Looks like a blue wire goes from each pin 8 to a red jack, and a black wire goes from both pin 8's to the black jack, and a 1R goes from the black jack to ground, yes? That means the red and black jacks are all tied together, and you have a common cathode voltage (on all three jacks) indicating total current for both power tubes. I'd remove the black wires and put 1R's from each red jack to the black one, and then run a wire from the black jack to the ground lug. Then you can check the cathode voltage and current on each side, red to black.

Taking a look at the Fender UL Twin Reverb I see they also used 2x 220u (stacked) for the reservoir, feeding 4x 6L6, so you should be fine there.

Regarding the hum, if the output tube balance turns out to be an issue, I have a plan to add another 10k bias pot that will fit right in. All you need to do is drill a hole.

On the filter, the treble side should be as effective as the bass, so I suspect some error here.

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Re: SSS a Hartman Manning Affair

Post by dreric » Fri Jan 12, 2018 6:02 am

martin manning wrote:
Wed Jan 10, 2018 6:25 am
Ok, I think I see what you have now. Looks like a blue wire goes from each pin 8 to a red jack, and a black wire goes from both pin 8's to the black jack, and a 1R goes from the black jack to ground, yes? That means the red and black jacks are all tied together, and you have a common cathode voltage (on all three jacks) indicating total current for both power tubes. I'd remove the black wires and put 1R's from each red jack to the black one, and then run a wire from the black jack to the ground lug. Then you can check the cathode voltage and current on each side, red to black.
Like this, (makes more sense)
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Re: SSS a Hartman Manning Affair

Post by martin manning » Fri Jan 12, 2018 7:27 am

Yes, much better. Now what voltages do you have on the power tubes and how closely do the cathode currents match? Measure pin 3, 4, 5, and 8 voltages, and also measure VAC on pin 5's to see how much ripple is in the DC bias.

Any luck on the high filter and presence?

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Re: SSS a Hartman Manning Affair

Post by dreric » Sat Jan 13, 2018 2:26 am

martin manning wrote:
Fri Jan 12, 2018 7:27 am
Yes, much better. Now what voltages do you have on the power tubes and how closely do the cathode currents match? Measure pin 3, 4, 5, and 8 voltages, and also measure VAC on pin 5's to see how much ripple is in the DC bias.

Any luck on the high filter and presence?
I did a quick test with the new power tube wiring, no change in hum. I'll measure voltages tomorrow.

In the meantime regarding the filters. I want to make sure that I am interpreting the schematic correctly. The low filter seems fine but the high does nothing. Are the poles of the rotary switch all connected together, then attached to the caps individually?
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Re: SSS a Hartman Manning Affair

Post by dorrisant » Sat Jan 13, 2018 3:03 am

dreric wrote:
Sat Jan 13, 2018 2:26 am
Are the poles of the rotary switch all connected together, then attached to the caps individually?
No...the caps are tied to a common buss. Then each one soldered to a pole. Each pole is separated from the bus by a cap. The common from the switch and the buss are looked at as the two ends of a capacitor. Think of it as a decade box, or substitution box for selecting the cap value you wanted.

No offense intended. I though your cap switch looked correct, from what I recall.
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Re: SSS a Hartman Manning Affair

Post by martin manning » Sat Jan 13, 2018 9:25 am

dreric wrote:
Sat Jan 13, 2018 2:26 am
I did a quick test with the new power tube wiring, no change in hum. I'll measure voltages tomorrow.
I didn't expect any change, but now you can get the individual cathode currents to help find the problem. It could be due to excessive ripple (there is always some) in the bias voltage and/or the current flowing on each side is too far out of balance and the ripple voltage isn't being cancelled in the OT. How much hum is there?

Also please measure the positive and negative voltages out of the bias supply. Those should both be about 160V from ground.
dreric wrote:
Sat Jan 13, 2018 2:26 am
In the meantime regarding the filters. I want to make sure that I am interpreting the schematic correctly. The low filter seems fine but the high does nothing. Are the poles of the rotary switch all connected together, then attached to the caps individually?
The switches have a single pole (the center terminal) with a moving part that can be rotated to connect it to one of the seven position contacts. Each cap is wired from a position contact to a common circuit node that is not on the switch (a bus). As Tony said, the switch just places a different cap in the circuit at each position.

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Re: SSS a Hartman Manning Affair

Post by dreric » Mon Jan 15, 2018 12:06 am

I think I found the hum origin. It had started to come and go. The hum changed as I manipulated the bias pot. Then I found weak connection on pins 6 and 4 on the right power tube. I got the connection to stay strong then measured the following voltages, while there was no hum:

All in in volts DC

Bias: -62.5
Bias +: 163.3
Bias - : -162.7

Right 6550

pin 3: 482
pin 4: 482
pin 5: -60
pin 8: 37.0


Left 6550

pin 3: 482
pin 4: 481
pin 5: -60
pin 8: 37.2

V1
pin 1: 225
pin 6: 221

V2
pin 1: 249
pin 6: 250

V3
pin 1: 431
pin 6: 431

V4
pin 1: 242
pin 6: 244

V5
pin 1: 315
pin 6: 301

V6
pin 1: 162
pin 6: 162

So fingers crossed I think I found the cause of the hum.

FET is fixed, mis wired pot

Presence I need to go through again, I took values from #124 wiring seems right...............

The high filter. After my near break down where I lost confidence in my ability to read a schematic I realized I've been looking at this thing to long. I just can't see the error. Could be a bad rotary switch. I want to build another set of filters to go in my #002 build, cause they suck. I'm thinking of building the second set and posting as I go, maybe the error could be found that way.
Eric
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martin manning
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Re: SSS a Hartman Manning Affair

Post by martin manning » Mon Jan 15, 2018 2:04 am

Great news about the hum. Voltages look reasonable. The idle current looks very well matched, but a little cool. I think I would dial it up to ~50 mA (assuming the 0.037 you list for pin 8 voltage is in mV). It should be easy enough to check the high filter switch function by measuring resistance from the center lug to the position contacts- it should be infinite except zero ohms at the selected position.

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Re: SSS a Hartman Manning Affair

Post by dreric » Mon Jan 15, 2018 4:56 am

The switch tests OK. Can you see anything I'm missing in the wiring?
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Re: SSS a Hartman Manning Affair

Post by martin manning » Mon Jan 15, 2018 8:09 am

The shielded wire connected to the low filter pole (the output lead) should be connected to the high filter pole (only the 270k should be connected at the low filter pole). The way you have it, it will definitely be all about the bass.

#124 values for the presence should be fine for a start, just add 2k pot in series with a 1u cap paralleled with the 270 ohm PI tail resistor shown in the Hartman schematic.

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Re: SSS a Hartman Manning Affair

Post by dreric » Tue Jan 16, 2018 1:04 am

I got all the repairs done.

Unfortunate, when I power up the only signal that is coming through seems to be the reverb return. The amp is only working at a fraction of its volume and the tone control seem ineffective. I'm wondering if I have a stray wire clipping shorting something out ???
Eric
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Re: SSS a Hartman Manning Affair

Post by martin manning » Tue Jan 16, 2018 1:09 am

Rats. It's really fighting you! I'm sure that was the problem with the filters. At this point I'd look for where the signal is lost with a scope or a listening probe.

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Re: SSS a Hartman Manning Affair

Post by dreric » Tue Jan 16, 2018 2:27 am

martin manning wrote:
Tue Jan 16, 2018 1:09 am
Rats. It's really fighting you! I'm sure that was the problem with the filters. At this point I'd look for where the signal is lost with a scope or a listening probe.
I agree, I'm going to step back for a day or so, clear my perspective

Just tolexed the cabinet.
Eric
1949 Zenith, Zenith Toggle Recoil, Zenith 55 & 440

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