Vintage *FAKE* Fender Amp

[thermionix]

The mustards and orange drops won't be leaky.  It was the filters I was concerned about.  Also, half wave rectified B+ is possible, but highly unusual and downright silly.

the schematic has .005uF input cap with what I consider to be pretty low grid to ground of 270k and you pretty much have the same thing going on.  Except you don't have any grid stoppers.  I have three channels: 47k and two 470k, thinking about switching one of the 470k's to 68k for a more normal value and just bypassing the input cap.

It's not grid leak biased, is it?  Is there a cathode resistor or straight to ground?

[wavley]

The mustards and orange drops won't be leaky.  It was the filters I was concerned about.  Also, half wave rectified B+ is possible, but highly unusual and downright silly.

the schematic has .005uF input cap with what I consider to be pretty low grid to ground of 270k and you pretty much have the same thing going on.  Except you don't have any grid stoppers.  I have three channels: 47k and two 470k, thinking about switching one of the 470k's to 68k for a more normal value and just bypassing the input cap.

It's not grid leak biased, is it?  Is there a cathode resistor or straight to ground?

It's not grid leak biased, it's got a bypassed cathode, and 270k would be an awfully small grid leak resistor.  My input stage looks exactly like has drawn, but mine has grid stoppers.  The 525 is just a supro thunderbolt with a different tone stack, I'm going to make a few tweaks and live with the tone stack a little longer because it is so different than everything else I have, but will probably end up switching to a thunderbolt tone control and maybe using the unused control as a master volume or something.

That's why I thought it was funny that I was staring at the schematic for my amp when he posted the schem for his Femder it had very close to the same input topology.  Where they differ is while the Femder doesn't have any grid stoppers, I have 470k on two of the three inputs and 47k on the outputs, which is a bit excessive in my opinion.  I'm going to switch one of the 470k to 68k and parallel the unused input triode before I make a decision about tweaking the outputs.

[vigilante397]

Push-Pull requires a different output transformer right?  And your driver tube will have to be rewired as a paraphrase phase inverter if you want to be push-pull.  If your current transformer can handle it maybe you could try just a second EL84 in parallel single ended for a bit more.

Correct and correct. I'm not positive the current power transformer could handle another tube, but I wasn't really planning on modding this amp to be push-pull, I want to keep this one as-is as much as possible (I probably will swap the ceramics and check everything else for leaking just for fun, and replace if necessary), but I like the design and I want to experiment with building based on this design. I found a pretty cheap American supplier for transformers so I'll probably get a single ended and push-pull and experiment with configurations until I find the sound I like at a power level I can use

[wavley]

Push-Pull requires a different output transformer right?  And your driver tube will have to be rewired as a paraphrase phase inverter if you want to be push-pull.  If your current transformer can handle it maybe you could try just a second EL84 in parallel single ended for a bit more.

Correct and correct. I'm not positive the current power transformer could handle another tube, but I wasn't really planning on modding this amp to be push-pull, I want to keep this one as-is as much as possible (I probably will swap the ceramics and check everything else for leaking just for fun, and replace if necessary), but I like the design and I want to experiment with building based on this design. I found a pretty cheap American supplier for transformers so I'll probably get a single ended and push-pull and experiment with configurations until I find the sound I like at a power level I can use

I just built a single ended, wired the output universal, and put a 470R cathode resistor in so everything will bias up (sure bigger tubes are biased a bit cold, but I played with it and the ability to swap to any tube trumped the marginal difference it made in this amp).  I used the 25 watt OT from Weber and it sounds really fantastic and loud enough to use with a reasonable volume band.  I'm really enjoying the elegance of simple amps that have all the parts balanced.  For me it was a two tube amp with a tweed tone control and a post driver master volume, it's really the first master volume that I haven't just put on 10 to pretty much take out of the circuit.  I was thinking about building the same amp with parallel single ended output tubes for more omph, we'll see if I get the time. 

That's why I'm revisiting my Harmony 525, I've just been using it as a low volume studio bass amp (my 70's Japanese Hofner copy sounds really great through it) but I think I can heat it up into being a great guitar amp and it will still make a good studio bass amp.  Like I said, our input stages are fairly similar so I'm following this pretty closely to see your results.  I actually really like cheap tube amps from the 50's, 60's, and 70's... sure most of them are kinda one trick ponies, but that trick is so different than the classic Fender and Marshall tones.  The other little amp I really love is the Kalamazoo Model One and Two.  I had a One, sold it to a guy and kinda regretted it, got a Two at the shop, made the right business decision, modded it and sold it, now that guy bought my old one and has both now!  Just to tease me he brought it up yesterday so I could order a Weber speaker for it and so it's sitting next to my bench.

[vigilante397]

I hate to necro-bump this thread after it's been dead over a year, but I still get to thinking about this amp sometimes when my mind wanders. I've made a couple mods recently as well. It now has a Tone Tubby Red Alnico speaker (LOVE LOVE LOVE this tone), I swapped one of the resistors in the tremolo circuit for a pot so I can control the tremolo speed as well as the depth, and I made a faceplate for it with my new laser engraver.

But I'm still puzzled as to the origins and age of the thing. I said over a year ago that I would double check the origins of the components and never did, until tonight, when I verified that everything with a label on it is Sprague. All the electrolytics inside, the orange drops, and the multi-section can are all Sprague. I was able to get the model number off the can, a Sprague TVL 4773, and it looks like there might be a date code on the bottom (7839L), but I'm not positive that's what it is. The output transformer says "LION" 5K REG. PHIL PAT. OFF, but I can't figure anything out there. Power transformer is stamped with GENERAL TRANSOFMER, no label or anything. I'm really kicking myself for throwing away the original pots, they may have had some secrets to tell But that was 4 years ago, what can you do now.

Anyway, here are some pictures of the cap and the transformers, do any of these mean anything to anyone?

[vigilante397]

Small update (in case anyone is still following this), a quick Google search shows that REG PHIL PAT OFF means registered in the Phillippines patent office. So American caps, Japanese tubes and speaker, Phillippine output transformer?

[Fender3D]

...Phillippine output transformer?

... mmh did the builder take home some souvenir from his sex tour?

[thermionix]

So American caps, Japanese tubes and speaker, Phillippine output transformer?

Don't forget the mustard caps (Mullard/Philips) which are European.  To my knowledge those were made in England and Spain.  I think you have somebody's homemade amp.  There is probably no way to tell where it was made.  7839 is quite possibly a date code, 39th week of 1978.  That's well after the Vietnam War, so it wasn't a Filipino trying to sell a cheap "Fender" to some GI (that kind of stuff happened a lot back then).

[vigilante397]

I think you have somebody's homemade amp.

I agree, it definitely seems that way. But I just wish I could get some answers the guy I got it from has been on a LOOOOOT of drugs as long as I've known him so I doubt he would be any help. Again none of this is crucial information for me to have, I'll he keeping the amp regardless, I just get so darn curious!

[stallik]

On the other hand, having the answers would draw a line under it. There's something romantic in the mystery - it just might have been used by......

[Hatredman]

On the other hand, having the answers would draw a line under it. There's something romantic in the mystery - it just might have been used by......

What about the Femder logo, did you do something with it?


--
Scarlett Johansson uses a Burst Box with her Telecaster.

[vigilante397]

What about the Femder logo, did you do something with it?
[/quote]

Not yet, it's still just sitting on my workbench. I was thinking about cleaning it up and re-doing the paint, bring it back to its former glory