Hoffman Amplifiers Tube Amplifier Forum

Other Stuff => Solid State => Topic started by: TIMBO on March 28, 2017, 04:46:14 am

Title: Correct speaker load
Post by: TIMBO on March 28, 2017, 04:46:14 am

Hi guys, I got a SS amp that I think was made in the 80's and as usual no info.
It's in sorta working order, scratchy pots.
It has had a speaker change and they have used a 4ohm 350w sub woofer.
This seems to work but I have no way of knowing if 4ohms is the correct speaker load or power rating.
It has 2/2N3773 power transistors.

I could guess that it's about 65w as the model is PS65  :dontknow:

Title: Re: Correct speaker load
Post by: shooter on March 28, 2017, 10:34:29 am

IIRC most transistor amps were designed to handle speaker loads down to 2ohms.  I don't know about "optimum", without docs, it's probably trial n error.

Title: Re: Correct speaker load
Post by: pompeiisneaks on March 28, 2017, 01:31:44 pm

Here's an item that has 2n3773's and seems to imply it uses 4w impedance. 

~Phil

Title: Re: Correct speaker load
Post by: smackoj on March 28, 2017, 09:21:16 pm

I agree with Shooter; SS amps are usually stable at 4 ohms or even less. If you look at any modern SS bass amp, they always label the output with something like: "160 watts into 4 ohms"  and  "100 watts into 8 ohms"

Title: Re: Correct speaker load
Post by: TIMBO on March 29, 2017, 04:37:45 am

Thanks guy's, I'm sure it's a bass amp.
Sounds OK with guitar plugged in.
I'm going to replace all the pots, some have real problems.

Found a date of may 83 on the PCB.
Trying to find a cheap 100w 4 ohm speaker.

Title: Re: Correct speaker load
Post by: TIMBO on March 29, 2017, 04:24:07 pm

Hi guys, Found this in the schem library.
http://el34world.com/charts/Schematics/files/_Miscellaneous/HH%20MA100.pdf (http://el34world.com/charts/Schematics/files/_Miscellaneous/HH%20MA100.pdf)

Not exactly the same circuit but pretty close.

Maybe an 8ohm will drop the output to a more useable wattage.

Title: Re: Correct speaker load
Post by: pompeiisneaks on March 29, 2017, 06:46:18 pm

Quote from: pompeiisneaks on March 28, 2017, 01:31:44 pm

Here's an item that has 2n3773's and seems to imply it uses 4w impedance. 

~Phil

Weird my link didn't seem to show up and I've lost it now, /sigh I probably forgot to paste it lol.

Title: Re: Correct speaker load
Post by: TIMBO on March 29, 2017, 08:58:18 pm

All good. Thanks mate

Title: Re: Correct speaker load
Post by: TIMBO on March 30, 2017, 02:47:36 am

Thanks guys, converted this bass combo to guitar.
(http://i761.photobucket.com/albums/xx254/Timbo-08/001_34.jpg) (http://s761.photobucket.com/user/Timbo-08/media/001_34.jpg.html)
Cab cleaned up well
(http://i761.photobucket.com/albums/xx254/Timbo-08/004_20.jpg) (http://s761.photobucket.com/user/Timbo-08/media/004_20.jpg.html)
All original components, reverb tank at the back.
(http://i761.photobucket.com/albums/xx254/Timbo-08/006_16.jpg) (http://s761.photobucket.com/user/Timbo-08/media/006_16.jpg.html)
A few fancy knobs.
(http://i761.photobucket.com/albums/xx254/Timbo-08/008_13.jpg) (http://s761.photobucket.com/user/Timbo-08/media/008_13.jpg.html)
Passive FX loop.
(http://i761.photobucket.com/albums/xx254/Timbo-08/009_19.jpg) (http://s761.photobucket.com/user/Timbo-08/media/009_19.jpg.html)
Some new pots.
(http://i761.photobucket.com/albums/xx254/Timbo-08/015_8.jpg) (http://s761.photobucket.com/user/Timbo-08/media/015_8.jpg.html)
(http://i761.photobucket.com/albums/xx254/Timbo-08/019_4.jpg) (http://s761.photobucket.com/user/Timbo-08/media/019_4.jpg.html)
An Eminence 100w 8ohm seems to work well.
I wasn't sure what a Solid State Bass would sound like for guitar use, a great result.
Both channels are clear without any flabbiness or muddiness.

A very usable amplifier.

Title: Re: Correct speaker load
Post by: smackoj on March 30, 2017, 10:23:26 pm

That is a nice piece. I like the liberal use of shielded cable. Looks first rate. Have you tried any effects with it? Just curious.   :icon_biggrin:

Title: Re: Correct speaker load
Post by: TIMBO on March 31, 2017, 02:39:38 am

Not yet, will do