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

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

The second symbol is a dpdt switch.

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

Quote from: radio on November 19, 2017, 11:25:38 AM
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

Quote from: sbirkenstock on November 19, 2017, 12:09:46 PM

Quote from: radio on November 19, 2017, 11:25:38 AM
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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> 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.

Quote from: PRR on November 20, 2017, 09:33:20 PM
> 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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> 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.

Quote from: PRR on November 21, 2017, 12:56:54 AM
> 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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Interesting how HK use a number of different speaker sims.

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

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