This amp could have been glorious, now it's just another half-done POS. OTHER than the circuit. That was the only thing the budget allowed to get satisfactory. This is why I'll completely reject any silver face half-measures from now on. Either go the whole-hog or go to the hacks in the next suburb.
Hey Brad - your style and delivery are refreshingly direct, and I'm gobsmacked by the knowledge and the skill, care and attention you give everything. Pretty rare these days I guess. If ever my old Bad Cat Cub needs an amp doctor I'll gladly drive the 10 hours or so to put her in your care. Take it easy old boy!
I'm about to restore a 1976 SF DR that I own which has an eyelet board in similar condition. I'm going to replace the eyelet board with a new one though. Great work on your part to clean this amp up so well.
It the royal WE . Set and match. Love the cone cry much more musician oriented than the techie voice coil rub . Often the goal is communication so one need to know the listener to be able to tell them thing they understand. Fine job there Brad.
Looks like Sam gave you the stank face of approval at 24:42 👍. Given the budget constraints, I think this one came out great. A dead amp breathes new life again
A fiberglass-bristle scratch-brush works very well for cleaning that sort of oxidation/corrosion from the speaker terminals, and any little bits of glass fiber that break off are nonmagnetic and therefore won't get sucked in by the magnet. PS, I assume you replaced the mangled pilot light jewel....
Great job Brad.. I know you wanted to do more, but there's no accounting for owners tastes eh ! 😅 I had a good laugh when you discovered that screw imbedded in the dust cap ..
EPIC and I say again EPIC amount of work. I'm in AWE. Although I knew you would do it justice, just taking it on makes one question your thinking. That said, I love it when any vintage amp gets a second chance. Kudos and much respect. Somebody donate some speakers. They're done. They will eventually F**k the amp and ruin your work plus they sound like...I won't say it.
Cleaned up so nice. Once again ur customer should apresiate ur OCD. But in the end this is whats will last. Good job, again. I would leave any amp in ur hands.
GZ34/5AR4 is an excellent rectifier. Fender used them in their Blackface Super Reverb Amps. I reckon Leo went to the 5U4 as a cost saving measure. It uses about 50% more filament current, heats up faster, but has more voltage drop at the plates when providing the same current. Also, the maximum current in the 5U4 is less than that of a GZ34. I think you were wise to not replace the GZ34 with a 5U4 just to make it 'correct' for a Silverface.
That celestion speaker seems a little too bright for this amp, but the amp itself sounds very good and I could picture Dick Dale or Link Wray playing through it. Considering the screw stuck through the dust cap, perhaps even Roy Buchanan would approve, because it would've added a nice raspy buzz or fuzz tone and Roy was once known to slit speakers with a razor blade and dunk them in water so tgat the cones would warp ---- this was in the days before fuzzboxes were available. The speakers are so faded and the grill cloth so degraded that it appears the front of the amp was sitting in direct sunlight for years.
Don't play too loud, or that grill cloth will vaporize! You are right, though, that amp deserved a full teardown and refurbishment. But it has a certain charm, nonetheless. You look at it and expect a vintage tone!
Hey Brad, doing some upgrading of components for AB763 for a 1975 SFSR w mstr volume. Will be reusing the stock 1M mstr vol pot (w/o boost) post-phase inverter. I previously changed the bias pot from bias balance to bias level. I moved the 220K neg bias resistors from the eyelet to avoid the induced voltage but is it necessary to add the trim pot and just Y the 220Ks off the board to the bias pot? If you think the trim pot method is best (JJ power tubes) what size trim pot were you using ?
Hi Brad, Intresting video! What are the values of the resistor and trimpot on the bias balance pot? Sorry, i am colorblind and think to see brown black brown (100ohm) for the fix resitor. Thank you in advance!
1k resistor and 25k trimpot, mate. That put this particular set in a range to max out at around 70%, so safe if some nuffy adjusted it without measurement. You results may vary depending on various factors.
😅😅😅 👍I know exactly who you're referring to! Also, in the spirit of alternate RU-vid channel amp-repair inclusiveness, no conspiracy theories here either! 🤔🙂
Come on Brad. Its was a joke. I really enjoy the videos. My back ground is in RF. Im retired now but enjoy learning about audio gear.@@BradsGuitarGarage
No worries Mony, I forgot your name but I remember it now. Sorry, I've been dealing with some seriously dumb comments recently as the channel grows. Maybe I should have just kept it under 1000 subs. LOL!
A thought on your tight twisted-pair speaker wire: this likely adds a fair bit of capacitance and inductance to the cable (and probably makes the wiring at least 50% longer than if you didn't twist them, which means there's some additional inline resistance as well). Is that really a good idea for speaker wiring? It might induce some low and high frequency rolloff, and perhaps induce oscillation in a tube amp if it wasnt 100% stable.
@@PsionicAudio I usually just use ordinary 18 or 20 gauge zip lead speaker wire, and mechanical rigidity isn't that big a deal when the wire runs are so short from speaker to speaker or back to the amplifier. Unless , of course,, somebody feels that it really needs to look original. This particular amp is so far from original condition cosmetically I don't know that it matters!
