Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on August 10, 2016, 04:18:52 pm

Title: Which Trem?
Post by: TIMBO on August 10, 2016, 04:18:52 pm

Hi guys, Got another vintage Aussie amp on the bench.http://www.guitargear.net.au/discussion/index.php?topic=47211.0 (http://www.guitargear.net.au/discussion/index.php?topic=47211.0)
It has had some mods done to it, mainly the TREMOLO.
I was wondering why it was changed from the original, is the LDR/Neon a better option compared to the original?
(http://i761.photobucket.com/albums/xx254/Timbo-08/001%203_19.jpg) (http://s761.photobucket.com/user/Timbo-08/media/001%203_19.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/002%203_12.jpg) (http://s761.photobucket.com/user/Timbo-08/media/002%203_12.jpg.html)

Title: Re: Which Trem?
Post by: PRR on August 10, 2016, 07:53:57 pm

The low-level cathode injection thumps like a dog in the dryer.

(You or) The Designer drew it oddly. The double 0.022+470K C-R-C-R network "belongs" in the tremolated plate to reduce the thump.

LDRs arrived at the end of the 1950s. There was a fad to use them. In this case I would lean to the LDR because low-level cathode injection is never quite satisfying.

Title: Re: Which Trem?
Post by: TIMBO on August 10, 2016, 08:51:02 pm

Thanks PRR, YEP connected to wrong cathode.
I'll leave trem wired as is and see what it sounds like when I get back together.

Title: Re: Which Trem?
Post by: TIMBO on August 27, 2016, 06:27:19 pm

Hi guys, the new chassis have arrived, so I need to sort the trem.
The idea of the roach style trem is a stayer and I found the Maton SRG150 has the same trem as the Fender Tremolux. http://el34world.com/charts/Schematics/files/fender/Fender_Tremolux-AA763-schematic.pdf (http://el34world.com/charts/Schematics/files/fender/Fender_Tremolux-AA763-schematic.pdf)
I just need a bit of guidance on how it should be connected.
I'm thinking of connecting the intensity pot to single input3 channel as per sheet 4
I notice that the circuit also is connected to the bias supply, can that be deleted as there is no bias supply in this circuit.

Title: Re: Which Trem?
Post by: TIMBO on September 10, 2016, 06:09:38 am

Hi guys, Completed wiring and got some nice sounds.
(http://i761.photobucket.com/albums/xx254/Timbo-08/006%205_2.jpg) (http://s761.photobucket.com/user/Timbo-08/media/006%205_2.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/007%203_6.jpg) (http://s761.photobucket.com/user/Timbo-08/media/007%203_6.jpg.html)
Voltages look good.
As PRR said thumping tremolo may be a problem and he was correct, it does work to a point but I think that other trem designs sound and work better.
I was going to use the LDR/NEON approach but this also was a bit beyond my knowledge to design.
The amp has an umbilical cord that connect the two chassis and there is an extra wire that can be used to convert it to a bias trem.
To do this I may need a bit of guidance on the trem circuit as most of circuits I have used only use one triode.
(http://i761.photobucket.com/albums/xx254/Timbo-08/001%207_7.jpg) (http://s761.photobucket.com/user/Timbo-08/media/001%207_7.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/002%206_8.jpg) (http://s761.photobucket.com/user/Timbo-08/media/002%206_8.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/004%205_3.jpg) (http://s761.photobucket.com/user/Timbo-08/media/004%205_3.jpg.html)

Title: Re: Which Trem?
Post by: TIMBO on September 25, 2016, 12:32:57 am

Hi guys, I think I have nutted this trem out.
Using the LDR trem from Fender has worked well, with minor problems.
I'm using a 3M-RA for the speed that is providing a reasonable spread of speed, although it does not pickup much speed till full rotation and at full rotation the speed cuts out.

I don't have a 50k-RA intensity pot and using a normal 50ka, again the intensity only really kicks in till the last third of the rotation, will this improve with a 50k-RA pot.
(http://i761.photobucket.com/albums/xx254/Timbo-08/001%208_5.jpg) (http://s761.photobucket.com/user/Timbo-08/media/001%208_5.jpg.html)

Title: Re: Which Trem?
Post by: PRR on September 25, 2016, 10:46:46 am

> last third of the rotation, will this improve

Yes.

Or try the straight audio taper, but swap the outside wires, and mark it 10-0. If that gives a good feel, except backward, buy the RA pot.

Title: Re: Which Trem?
Post by: TIMBO on September 25, 2016, 01:52:23 pm

Thanks

Title: Re: Which Trem?
Post by: kagliostro on September 25, 2016, 04:08:18 pm

Build a reverse log pot if you need one

(http://www.geofex.com/article_folders/potsecrets/revlog.gif)

(http://www.geofex.com/article_folders/potsecrets/revser.gif)

http://www.geofex.com/article_folders/potsecrets/potscret.htm (http://www.geofex.com/article_folders/potsecrets/potscret.htm)

Ciao

Franco

Title: Re: Which Trem?
Post by: PRR on September 26, 2016, 04:58:48 pm

> potscret.htm

Does not work except for straight potentiometer use.

The Fender LDR is wired different. The pad resistor will just kill signal.

There ARE reasons reverse-audio pots exist.

Title: Re: Which Trem?
Post by: TIMBO on September 27, 2016, 03:48:19 am

Thanks PRR, New pot on the way.