Triode Dick's KT88 PP Amp.

[juoto]

Hello everyone!

First of all, sorry my bad English.
I'm typing here in Finland...winters coming...

Anyway, I'm building Triode Dick's KT88 PP Amp in stereo.

i'd like to know what are the resistors R17 and R18 in The chema?
Are they 1R and what wattage?

Thank's a lot, if anyone can help me littlebit!

Juha from Finland.

http://members.home.nl/triode.dick/Bill/schema_versterker.GIF

 

[ballpencil]

It says there on the schematic they are 1 ohm. It's fixed bias and the 1 ohm resistor is to measure the bias current (60mA x 1ohm = 60mV). Power rating can be 0.25W (60mV x 60mA is very small).

 

[juoto]

OK! Thanks a lot!

Juha

 

[fdegrove]

Hi,

If you plan to build a single stereo unit you could also use each half of the 6SN7.
Just put 2 47K resistors in series (2W each is ample) for the anode load and 1K iso 500R for the cathode R.

UGT is short for Uitgangstrafo in Dutch which is the Output transformer as I assume you guessed already.

As for measuring the current across the 1R resistors, you could add the test points on the top of the casing for easy access.

Cheers, 😉

 

[jazz]

Hi,

Sorry to contradict but those resistors 1R (yes 1 Ohm) should be rated at 1W at least as noted in dutch tekst on the schematic on the downside of the page in red: 'all resistors are rated at 1W unless otherwise noted'.

These resistors will see varying current and at that position some overkill is sensible.

regards,
Joris

 

[rayma]

It says there on the schematic they are 1 ohm. It's fixed bias and the 1 ohm resistor is to measure the bias current (60mA x 1ohm = 60mV). Power rating can be 0.25W (60mV x 60mA is very small).

However, if a tube shorts the current can be much larger. I always use at least a 1W part here, to avoid damage in the event of a short.

 

[juoto]

Allright!

Thank's guys!

Now I have another question...
I'm building this amp to my friend, and He would like to have subwoofer out connection in the rear panel.

Obviously signal level must rise when volume is rising and right and left channel must be summed to get one RCA-out. Lowpass-filter in no needed, because subwoofer allready have that.

Any suggestions?

Thanks again!
Juha

 

[SpreadSpectrum]

However, if a tube shorts the current can be much larger. I always use at least a 1W part here, to avoid damage in the event of a short.

Wouldn't you want the resistor to blow out in the even of a short in the tube so as to possibly save the output transformer windings? I would choose a resistor with a low power rating with the hope that it would burn up in the event of a short.

Better yet, you could put a fuse in to protect the output transformer in the case of a short.

 

[fdegrove]

Hi,

Should your friend use a CDP as his main source then this variation is actually better suited; it will drive the Schmitt splitter directly.

Cheers, 😉

 

[scott17]

...He would like to have subwoofer out connection in the rear panel.

Check out post #8 here:
http://www.diyaudio.com/forums/solid-state/208473-simple-subwoofer-buffer-summer-circuit.html

 

[rayma]

Wouldn't you want the resistor to blow out in the even of a short in the tube so as to possibly save the output transformer windings? I would choose a resistor with a low power rating with the hope that it would burn up in the event of a short.
Better yet, you could put a fuse in to protect the output transformer in the case of a short.

I would size the screen resistors to act as a fuse. For example, 100 Ohms, 1 W seems to work ok in my experience.

 

[fdegrove]

Hi,

Forgot to insert the link:

http://www.triodedick.com/monobill_2/monobill_2_schema_versterker.GIF

Cheers, 😉

 

[ro9397]

What is this amp's power output?

Tx!

 

[painted]

>50W pc