Need help with the schematics of the Hughes & Kettner Tubeman 1

[sbirkenstock]

High Everybody,

just digged out my old Hughes & Kettner Tubeman 1, since a friend insisted it sounds the best...
And surprisingly it does sound execellent, so I wonder why I put it in storage....
However, wanted to figure out some things and searched for the schematics.
I have some questions on this:

a) on the top in the middle there is something that looks like a rectifier.
I figured out that this are the clipping diodes and that it has 4 diodes each way going to ground.
This layout just saves 2 diodes, so you need "only" 6 instead of 8.
Is this correct?

b) on the left side a bit higher than in the middle, on top of the text: "Board1, TSM 2.--, Mid Boost" there is a symbol I can not find.
Kind of two bars with 4 circles.
It has the number 3 on the left side.
What is that?

c) The schematics has "TSM 2" several times over it.
Any idea what it stands for?

Best regards,

Stephan 





Link to schematic:
https://plus.google.com/photos/105522823743827842245/albums/5275624603790551905/5275624657196258226?banner=pwa&pid=5275624657196258226&oid=105522823743827842245

[radio]

No it IS a rectifier, not clipping diodes,nothing to change here.

I have the Tubeman 1 ,but as its still working I never opened it.

Good luck with it , I used it alot apart the jazz setting

[FiveseveN]

The second symbol is a dpdt switch.

[J0K3RX]

TSM 2 is the daughter board that has the tube and all the pots on it.

[sbirkenstock]

No it IS a rectifier, not clipping diodes,nothing to change here.

I have the Tubeman 1 ,but as its still working I never opened it.

Good luck with it , I used it alot apart the jazz setting

I do not think it is a rectifier, since it is connected to ground and not to an AC source.
The other side is connected to the signal (going to the gate of tube 1)

I think this setting is the "Rock" setting, so clipping diodes would make sense.

I got myself a second Tubeman, and both have very "shaky" pot connections, guess since they are soldered directly to the daugherboard and it kind of physically pulls something.
Same for you?

Stephan

[radio]

No it IS a rectifier, not clipping diodes,nothing to change here.

I have the Tubeman 1 ,but as its still working I never opened it.

Good luck with it , I used it alot apart the jazz setting

I do not think it is a rectifier, since it is connected to ground and not to an AC source.
The other side is connected to the signal (going to the gate of tube 1)

I think this setting is the "Rock" setting, so clipping diodes would make sense.

I got myself a second Tubeman, and both have very "shaky" pot connections, guess since they are soldered directly to the daugherboard and it kind of physically pulls something.
Same for you?

Stephan

I left it on rock setting since I like that one most . Years ago I read in a german forum they had to change the poor quality pots as they crackled


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[PRR]

> I do not think it is a rectifier

It is "8 diodes" for +/-2V clipping. Except it uses a short-cut equivalent using 4 of the diodes both ways, so it only needs 6 diodes total. And then they get the 4 diodes pre-made as one part ("a rectifier") which may be cheaper than 4 diodes, either to buy or to assemble.

[radio]

> I do not think it is a rectifier

It is "8 diodes" for +/-2V clipping. Except it uses a short-cut equivalent using 4 of the diodes both ways, so it only needs 6 diodes total. And then they get the 4 diodes pre-made as one part ("a rectifier") which may be cheaper than 4 diodes, either to buy or to assemble.

Ah learned sth!

But wouldn't it be easier to use four leds??



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[PRR]

> But wouldn't it be easier to use four leds??

LED is 4 cents. Diode is 1 cent. FWB is 4 cents.

That makes the 2D+FWB cheaper than 8D or 2LED (or 2FWB).

If a part is used a LOT, the cost is lower. Those diodes are used like salt in canned food- a lot.

There's cost for board space. Every part-type has a cost to keep it in a bin in inventory. There are only so many slots in the robot for parts. There's a cost every time the robot arm places a part. Full cost accounting is tedious, and we can't really know all the costs. But it looks like someone working for H&K spent hours shaving pennies on this design.

> But wouldn't it be easier to use four leds??

Look at the 100K series resistor. This thing clips at low-low current. LEDs are not tested for low-low current leakage. I have had trouble with that. Plain diodes are specified for low-low current leakage.

Why not run larger current? It might cause clipping transients on the power rails. This can be filtered. That would add cost. Again I suspect someone spent many hours weighing all these choices to shave-out every last part-penny.

[radio]

> But wouldn't it be easier to use four leds??

LED is 4 cents. Diode is 1 cent. FWB is 4 cents.

That makes the 2D+FWB cheaper than 8D or 2LED (or 2FWB).

If a part is used a LOT, the cost is lower. Those diodes are used like salt in canned food- a lot.

There's cost for board space. Every part-type has a cost to keep it in a bin in inventory. There are only so many slots in the robot for parts. There's a cost every time the robot arm places a part. Full cost accounting is tedious, and we can't really know all the costs. But it looks like someone working for H&K spent hours shaving pennies on this design.

> But wouldn't it be easier to use four leds??

Look at the 100K series resistor. This thing clips at low-low current. LEDs are not tested for low-low current leakage. I have had trouble with that. Plain diodes are specified for low-low current leakage.

Why not run larger current? It might cause clipping transients on the power rails. This can be filtered. That would add cost. Again I suspect someone spent many hours weighing all these choices to shave-out every last part-penny.

Thanks for the in depth explanation[emoji3]

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[Rob Strand]

Interesting how HK use a number of different speaker sims.

[Govmnt_Lacky]

That IS a 1.5A Bridge Rectifier.

B80C1500. Part number is right next to the part in the schematic.

Linky: http://pdf.datasheetcatalog.com/datasheet/wte/B380C1500.pdf

[radio]

I wonder if using the bridgerectifier would also work with a rat circuit,with less distortion of course?!