Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on January 07, 2017, 02:00:33 am

Title: Adding a Hot Switch
Post by: TIMBO on January 07, 2017, 02:00:33 am

Hi guys, Got a nice PA conversion and it's sounding great.
BUT there is a spare triode.
It would be a simple addon, but it's not a plexi type circuit.  :think1:
Might need a few ideas on where to insert it.

Title: Re: Adding a Hot Switch
Post by: kagliostro on January 07, 2017, 05:57:14 am

You have more than an option to use that spare triode

. LTPI

. Gain Stage between V1b and V2a

. Parallel with V1a

. "Fat" Stage in parallel with V1b

I would like to give a try to "Fat" Stage in parallel with V1b

something like here (with a separate pot for the Gain and for Fat - I prefer this version)

(http://el34world.com/Forum/index.php?action=dlattach;topic=13298.0;attach=28550;image)

or here (with only a pot for the Fat)

(http://el34world.com/Forum/index.php?action=dlattach;topic=9636.0;attach=15949;image)

Franco

Title: Re: Adding a Hot Switch
Post by: TIMBO on January 11, 2017, 04:22:25 am

Hi guys, I have found a good place to insert the hot switch. Found the Ampeg Gemini II a good candidate for an added triode.
I went with some traditional values for the anode/cathode resistors.
With 150k/3.3k seems to work well for a treble boost as well a volume boost.
But after reading some info on the plate/cathode resistor combo's, the info mainly was aimed at the 12AX7.
And these plate/cathode resistors combo may not really apply to the 12AT7.
My aim is to get a slight increase in volume and also a hint of hair.
In the normal mode this amp has this hint of hair to almost full volume and is awesome in the circuit as is.
Just looking for that extra bit with out getting too overdriven. :think1:
SHEET 6
 

Title: Re: Adding a Hot Switch
Post by: PRR on January 11, 2017, 05:27:04 pm

12AX7 bias/loading often works fine for 12AT7 doing the same job.

You can try AX values and also 1.5X the AX bias value to see if the "Mu-correction" is enuff difference to notice.

Title: Re: Adding a Hot Switch
Post by: TIMBO on January 12, 2017, 12:37:27 am

Hi PRR, I'm applying this as a guide http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/ECC83.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/ECC83.pdf)
I may be way off the mark..................
Should I be reducing the plate resistor to 47k and cathode per the plate voltage to achieve a type of distortion.
Rather than go the other way as I have per my schem???

Title: Re: Adding a Hot Switch
Post by: TIMBO on January 13, 2017, 04:33:38 am

Hi guys, Thought I'd try some "cold clipping"
Gives a slight volume boost with a bit of edge.
I think it has some potential.
I put it on the scope and the sine wave has the tops chopped off. :think1: at TP 1&2

Title: Re: Adding a Hot Switch
Post by: TIMBO on January 15, 2017, 03:33:06 am

Hi guys, Settled on a Cold Clipper stage as a boost/distortion with 100k/10k resistor combo.
(http://i761.photobucket.com/albums/xx254/Timbo-08/004_19.jpg) (http://s761.photobucket.com/user/Timbo-08/media/004_19.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/005_18.jpg) (http://s761.photobucket.com/user/Timbo-08/media/005_18.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/007%202_16.jpg) (http://s761.photobucket.com/user/Timbo-08/media/007%202_16.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/008_11.jpg) (http://s761.photobucket.com/user/Timbo-08/media/008_11.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/010_17.jpg) (http://s761.photobucket.com/user/Timbo-08/media/010_17.jpg.html)
Just for a bit info, the guys here had found that 100v line transformers work well.
http://www.altronics.com.au/p/m1130-40w-100v-line-pa-ei-core-transformer/ (http://www.altronics.com.au/p/m1130-40w-100v-line-pa-ei-core-transformer/)
And are well priced.
Used mainly with the 6DQ6 and 6CM5 with approx. 3.5k P-P

Title: Re: Adding a Hot Switch
Post by: kagliostro on January 15, 2017, 07:41:57 am

Nice :thumbsup:


Have you build the cabinet for the new use or the amp had it previously done ?


Franco


p.s.: I've understand, but please, post the new situation schematic (thanks)


is this the latest version ?


(http://i.imgur.com/UYImpA9.jpg)

Title: Re: Adding a Hot Switch
Post by: TIMBO on January 15, 2017, 01:09:05 pm

Hi K, Cabinet is new.
The schematic is the same as in reply#5, I have only changed the trim pot to 1M and the cathode resistor is 10k.

Title: Re: Adding a Hot Switch
Post by: kagliostro on January 15, 2017, 02:17:09 pm

Thanks TIMBO

Quote

Cabinet is new

Yes, but have you ordered it to someone or you build it ?


Franco

Title: Re: Adding a Hot Switch
Post by: silverfox on January 15, 2017, 02:21:00 pm

That turned out well. Nice clean build. What can you tell me about the scope you have? It looks like one of the newer digitals and I'm considering buying one in the near future. At this point in time I'm looking at a Pico scope I think it was called.

silverfox.

Title: Re: Adding a Hot Switch
Post by: PRR on January 15, 2017, 03:20:19 pm

Man, that really deserves a window.