1980 DR-504 needs TLC

[edvard]

Hello all. As I said in my "Introducing myself" post, I have recently acquired a 1980 DR-504, serial# 14947. The previous owner said the last time he played it many years ago, it made a buzzing noise and quit, and never got around to fixing it since then. I have an Accurate Instrument Co. Tube Tester Model 257 (consumer-grade, good for testing go/no go) and the power tubes tested at about halfway up the "good" section of the meter, and no shorts. Two of the preamp 12AX7s (er... ECC83s, sorry) were bad/borderline, lucky I have two rattling around in an old abandoned project that tested good. The caps look meh... could be bulging, could be simply old, I'll replace them before I go flipping the thing on. I discovered Mark Huss' page that proved invaluable for schematics, but the signal path for this amp looks different from schematics he has posted; at first glance, it resembles a "Late '70s 2-input" AP up front with "Bright" and "Normal" inputs, but it doesn't use the second triode of V2, like the SAP schematics show. Also, it has the "Canadian Mod".

What I plan to do:
- Clean it up (mostly already done)
- Re-cap with ARS caps (best I could find that didn't involve highway-robbery-level shipping charges, and had all the exact values)
- Flip it on and see how it roars (or not)

Questions:
- I noticed it doesn't use grid stopper resistors at V2 or V3, would this be recommended? Or does it sound just fine without, especially on higher-gain settings? It's an easily-reversed mod.
- The Partridge stickers came off the transformers as I was cleaning them up, due to the glue drying out. Any recommendations on what kind of glue to use to stick them back on?

I'll post more questions as I think of them, and I'll let you all know how it goes as soon as I can get new caps. I also took the liberty of modifying Mr. Huss' schematics to show how this one is laid out; see below:

DR_2InputPre_w_CA Mod_1980.gif (426.26 KiB) Viewed 2223 times

[mhuss]

I wouldn't worry about the grid stoppers until you try it out and see what it sounds like. I am not a fan of the CMod, it was a quick and dirty hack and sounds like it.

I have no advice to offer on glue.

[edvard]

Ha! Yes, I should see how it sounds first. My pedigree is in the heavier genres, so I'm only hoping for enough grit to work with. Without grid stoppers, I imagine it can get a bit "spitty" at higher-gain settings, so that was my idea to smooth things out without losing grind.
For the sticker glue, I think regular spray adhesive might do the trick, or maybe double-sided tape.
Also, genuine Fane cabs won't be within my budget anytime soon, has anybody found a "close enough" sound-alike? I read on another forum somewhere that "hi-fi" speakers would be closest, but I have no idea. All I have at the moment is a 12-inch 100W Carvin "British Series" that I got for cheap at a second-hand shop and built a cab for. I'm not rich enough to be picky.

[elcapitan]

Hello,
Regarding gluing the stickers back on:
I can't say for certain as I haven't tried this method myself, so full disclosure about trying at your own risk.
I have had surprisingly good luck with plain old white PVA "Elmer's" -type glue in the past for similar projects.

I like that it isn't solvent based or too aggressive, which I would worry would attack the label and or transformer varnish.
The PVA -style glue should be mild enough you don't need to worry about it reacting too crazy.
Just a very thin smear should do it, and blot off most of the excess before it sets. Just don't get carried away as it is water-based, but a small drop or two should do the trick I would think.

Option 2:
I have seen "reproduction" Partridge labels on Reverb from time to time. Can't vouch for the quality/appearance as I've never seen them in hand, but it may be worth looking at as well. Good luck!

[edvard]

Thanks for the suggestion, I thought of that too, but I was worried that the glue might not be "sticky" enough, and that kind of glue does dry out over time. But then again, so did the original glue, LOL.

[mhuss]

If you're more into heavy, the speaker you've got might be OK. Again, try and see.

[elcapitan]

Yes, the white glue isn't as "aggressive" as some other adhesives.
Worst comes to worst, you can always re-glue the labels back on if they fall off again a few years (or decades) from now!

Other options may be found at luthier supply houses:
-hide glue
-fish glue
Both are water soluble, dry clear and hard, and are fairly forgiving/easy to use.

(If it were my amp, I would avoid using a contact cement or rubber cement as these are solvent-based, and may react with/damage your label, and the original varnish on the transformer laminations. I have not had success with the "low-VOC" type contact cements, either. Waste of time and effort. )

[edvard]

If you're more into heavy, the speaker you've got might be OK. Again, try and see.

Good to know, thank you. At this point, I'm going to have to wait for a tax return to get new caps, so it won't be for another month or two. Can't wait!

[edvard]

Yes, the white glue isn't as "aggressive" as some other adhesives.
Worst comes to worst, you can always re-glue the labels back on if they fall off again a few years (or decades) from now!

Other options may be found at luthier supply houses:
-hide glue
-fish glue
Both are water soluble, dry clear and hard, and are fairly forgiving/easy to use.

(If it were my amp, I would avoid using a contact cement or rubber cement as these are solvent-based, and may react with/damage your label, and the original varnish on the transformer laminations. I have not had success with the "low-VOC" type contact cements, either. Waste of time and effort. )

I don't have easy access to hide or fish glue, and I have a pretty tight budget, so white glue it is. Thanks for the tip, I'll be doing that sometime soon while I wait for funds for a re-cap.

[edvard]

OK, I've tried to post 3 times, but the website times out on me every time, so I'll keep this one short and sweet, with no pictures.
Got new capacitors.
One power tube kept red-plating, so I got a new pair.
Sounds great, but not what I need, will be selling.
The end.

Maybe if I'm in the mood later, I'll try and make a longer post, but this has frustrated me to no end today. Good night.



P.S. White glue stuck down the stickers just fine. Thanks for the tip!