BTW, imho 5 Fender knobs look way better on this little amp than the bit smallish originals... just personal preference

Quote from: galaxiex on November 05, 2017, 07:30:42 PM
Interesting layout compared to the others.

All those iterations are a bit puzzling/amusing! :-)  ... why ?! 

QuoteCan you do a overall shot that shows the whole chassis.

Here we go, 3 more pics, have a good weekend!

Quote from: galaxiex on November 02, 2017, 07:34:00 PM
Just curious to see what it sold for.

Same here, it didn't do too bad I guess.

OK, FWIW, a few quick and low-qual pics for now, this is mine with the 'blue left front', and the reverb tank right behind the front panel.

Bye

Aha, that auction just finished, 8 bids, winning bid US $57,66

Perhaps better not using mine as a donor-chassis/enclosure ;-)

Hi,

Thanks for the pictures! Interesting to see that 'they' (assuming it was all coming from the same factory) went through all these versions, colour schemes, component re-locations etc 

Mine is with the reverb tank located between the front and the PCB, so all pots are wired, so not directly on the PCB.
No reverb-TX.

Here's another, let's see what it does within a few minutes, now at $41 with 2 minutes to go.
https://www.ebay.nl/itm/263282000680?ul_noapp=true


Bye & I'll post pics from my GA920P this weekend

Quote from: galaxiex on November 01, 2017, 06:48:49 PM

QuoteJust curious, how 'wet' can the reverb get at maximum?

It can get pretty wet, but it doesn't sound good. 
I'm sure this is due to the limitation of the small tank.
It also doesn't help that there is only 1 spring.

OK, too bad. Only 1 spring, I see. So that would actually mean that a better small tank could still give some room for improvement...  but like you say, it'd be unrealistic to expect Twin Reverb sounds, let alone the superwet stuff as from the Fender Reverb unit.

QuoteI played with part values in mine and got a "fair" sounding reverb,
but it will never be a Fender Twin.

If you "over do it" with driving the tank too hard,
or increasing the gain on the recovery side, bad noises happen.
Screeching/feedback/metallic "clank" sound, etc.

Changing some cap values and possibly adding some caps in strategic places can smooth out the sound.
Limiting the frequency range that is fed to the tank helps. 

Thanks for sharing the results of your experiments, much appreciated!

QuoteThere are other small multi spring tanks around that would fit the chassis.
I never tried any, and there may be impedance matching problems with some of them.
No guarantees they will sound any better than the existing tank.

I have a broken Danelectro Spring King, but the tank itself is assumed to be OK.
That's a two spring medium length one, still not Fender-close, but probably a step up.

I realized that this 'Dano tank' matches the Fender TR & Reverb unit specs, w.r.t. the in- and output- impedances. Not the length obviously
Adding say the Surfy FET Reverb PCB (you'll have heard of it) would easily fit this enclosure.

Bye!

Quote from: galaxiex on November 01, 2017, 06:51:23 PM
I don't recall the layout of the other amp.

Easy enough for me to open it up and get some pics.
I'll do that later. 

Cheers!

Nice, who knows it's like mine :-)  And who knows that other one has the right schematic of your first one, and vice versa :-)     

I'll post some pics as well (this weekend)

Bye!

Quote from: galaxiex on November 01, 2017, 12:58:53 PM

Yup, they are kinda cool little amps.  Actually sound pretty good for what they are.

Just curious, how 'wet' can the reverb get at maximum?

QuoteBe aware there are at least 2 different versions of this amp,
both have the same name (National) and model number (GA920P) but different circuit boards/schematics.

I have one of each but not posted anything about the "other one" yet.

Hi,

Thanks, I'll check the R_DC of the spring unit here as well.

Mine looks alike (outside & inside) to your pics on page 1 at first I thought, but the placement is actually drastically different.
The sping tank is directly behind the front panel and the power devices are mounted on the base of the unit. The rear jack panel location is also different. Perhaps this is exactly describing your other unit ;-)

Mine has the blue section on the front as well, I've seen some pics of amps without.  I don't have the speaker enclosure.

FWIW/IIRC, I recall these amps being shown in mailorder catalogs. Here in The Netherlands the combo version went for 199 (Dutch guilders), and there was a 'Hondo II'  Les Paul copy for another 199 to be had, same catalog page, got us drooling :-)

OK, I'll see if it works, and if so, how it sounds. Curious to the spring reverb configuration. Too bad the enclosure doesn't permit a full sized tank.

Bye!

Quote from: clintrubber on November 01, 2017, 09:05:23 AM
Was wondering, any info on the reverb tank they used ? Input- & output-impedances ?

Oops, apologies, just saw the 225R & 222R indications in the last version of the schematic. Are these as measured with a DMM ? So the R_DC values ?

Will check as well on my unit.

Bye/thanks

Thanks for sharing this info on the GA920P, much appreciated!

Have one here as well, no idea if it still works, I've never plugged it in after taking it home from a fleamarket (never dared to..., have to check it for safety first)

Mine didn't come with a schematic.

Was wondering, any info on the reverb tank they used ?  Input- & output-impedances ?
Then possibly another circuit could be used to drive the tank.

I'll admit I was intending to use the enclosure forsomething else, but who knows it's a fun amp by itself.

Bye/thanks   

Same here, can open it but lower part is missing. Still nice to find this, thanks! I have the GA920P.