Hola Z; nothing wrong w/ RadShaq but you may have some trouble with odd values and higher wattage ratings. If they no have, Antique Electronics Supply will; nothing less than .5 watt; greater if original has higher rating. It's possible that the unidentified pot is either a master volume for the trem or, considering that yours is an early model and the fact that the bias voltage runs through the trem 'strength' control, that it could be a bias control. If for volume, it would have been intended as a set-it-and-forget-it never-higher-than control; if for bias, we'd want to leave it alone for now leaving it as something to mess with if you can't get the trem de-thumped.zulu said:... Fuse was fine, but had the slightest wiggle at one end. testing between the fuse brackets produced the bb--bb--bbe-bbeeeeep. I'm pretty sure that took care of the intermittent problem. To quote a famous amp tech: "It's always something" L. Fender I'm going to change that one other cap on the speaker. Si; bueno. There are a number of resistors out of tolerance (Rad Shaq okay for those?), and I need to search up thread on "trem thump" that I found a while back.
It's possible that the unidentified pot is either a master volume for the trem or, considering that yours is an early model and the fact that the bias voltage runs through the trem 'strength' control, that it could be a bias control.
I think this is the bias supply filter cap that has been refreshed; can you confirm? + lead should be connected to ground ... as a general rule, bias circuits are the only place you find electrolytics with the + lead to ground:
As ever, there are bold amp techs and there are .... :wink: J
I'll check that this evening. Interesting. Ok.zulu said:1. how can I tell the wattage rating of a resistor.
In these old amps, everything 1 watt or greater is marked with its rating; everything else is .5 watt.
2. has that capacitor test worked well for you? OK to leave cap connected for ohm test I suppose?
If the meter has the setting, it's how they are tested; must disconnect one end ... in part why sometimes I lose patience and clear-cut ... in trem circuits I replace them all because the idea of my going in there again to replace another ... or making somebody else replace another when I could have done 2/3/4 just as easily ... everybody feels differently though ... some feel it's better to leave as much original as possible ... some say the world will end in fire ...
I played with it a little, couldn't get it to affect the sound. The two resistors connected to it are off tolerance (down 50%)It's possible that the unidentified pot is either a master volume for the trem or, considering that yours is an early model and the fact that the bias voltage runs through the trem 'strength' control, that it could be a bias control.
Well ... you know what to do with out-of-tolerance resistors...
[quote:3lys88le]I think this is the bias supply filter cap that has been refreshed; can you confirm? + lead should be connected to ground ... as a general rule, bias circuits are the only place you find electrolytics with the + lead to ground:
.. guys like Coastie?? [/quote:3lys88le]As ever, there are bold amp techs and there are .... :wink: J
When you and I grow up, we should both hope to be like Coastie; a view of a work-in-progress at Wuzzatronics Labs, the best ampworks on the south island;
In these old amps, everything 1 watt or greater is marked with its rating; everything else is .5 watt.
Hi Z; the higher rated resistors commonly found in the power supply; 7w, 10w, and 1w on the left (the 7w and 10w might be mis-ID'd vice and versa) ... you might have to bend/roll the resistor to see the markings. The 4th resistor ID'd at the bottom in dotted circle is at the reverb amp can capacitor ... not in either pic. On the right are several resistors that are probably 1w ... larger contrasted with all the carbon composition red and tan smaller ones. Not uncommon for amp and schematic not to match 100%. The ones one the right are probably plate resistors; used to drop the raw dc voltage to 125-175 volts for the tubes ... they are not directly in the signal path.zulu said:... didn't see any markings that I recognised. There are a few resistors that are dark red, with standard color bands, and a few that are larger than others.
I think this is the bias supply filter cap that has been refreshed; can you confirm? + lead should be connected to ground ... as a general rule, bias circuits are the only place you find electrolytics with the + lead to ground:
Hi Zac: that cap is typically used in conjunction with a resistor in parallel; is there a resistor there? That's the pinouts of a 6GW8 up top (ignore triode section to left) v. the schematic ... below; your cathode cap and a yet-to-be-confirmed / identified cathode resistor (in blue) v. a schematic for a Gibson GA19; a cathode-biased, Class B amp ... You also have a bias tap in the power supply - the brown twisted pair and somewhere a bias diode and filter cap ... if you have a resistor in parallel with that electrolytic cap, you have a belts-and-suspenders bias scheme :shock: <sigh>zulu said:... the power tubes are wired together at each one's pin 7 negative to a shared terminal, then to chassis ground.
. The four caps in red circles on the left are the four caps ID'd on the right; can't tell which is which but all four have to be functional. The green circle cap is a cathode resistor bypass cap; don't know if you changed this one or not; if not ... observing polarity; - to ground.
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Or ... if you wanted to sell it, you could say that yours is factory-equipped with Thumper ... formerly the hottest thing in built-in amp effects ..... maybe not :wink: My pleasure Zac.zulu said:Hi John. .... I think I need to trace whatever comes off the other tube at pin 7, maybe there is a resistor that terminates at the ground with that 22 uF cap. Does that make sense? Yes; makes sense - could go from 'other' pin 7 to ground. Might not be there but need to know. The amp ran over two hours last night. I'm quite sure that loose fuse was causing the intermittent problem. Yippie! Green circle cathode resistor bypass cap is one that I changed. OK. That trim pot there is the trem strength, or the way I see it, sets the 'range' of the trem strength on the front panel. Manipulating that pot I was able to eliminate the "trem thump" while maintaining a decent range of strength adjustment up front (IOW front strength knob full up, turn trim pot up until thump occurs, then back off a little). I'm debating on changing these now with the trem working good, although it would be interesting to see if new caps would provide increased trem 'strength before thump'; Ok; acts a little like a master volume ... a volume control in series setting the upper bound of the effect.
will report back.Yes; makes sense - could go from 'other' pin 7 to ground. Might not be there but need to know
you can say that again!Yippie!
:lol:factory-equipped with Thumper ... formerly the hottest thing in built-in amp effects
They are known as Bulgin connectors and again at Allied ... URL long form; http://www.newark.com/jsp/brand/brands. ... =TC|14596|{keyword}|{placement}|{ifcontent:C}{ifsearch:S}|b|{creative}&s_kwcid=TC|14596|bulgin||S|b|4482593236zulu said:... the speaker connection plugs ( I can't recall the name of those) aren't tight enough, a stiff breeze could blow the speaker plugs out of the chassis plugs. can they be pinched tighter, or should be replaced?
lol I keep waiting for capnjuan to say "phooey, you're on your own!" but until then....MAN are you guys still up? You've been at this all night! WH-O-O-O-AH... make that several nights!
she's sounding great John, I appreciate it so much.Hi Al; jes' trying to make sure Zac's Thunder thunders ...
Hi John. .... I think I need to trace whatever comes off the other tube at pin 7, maybe there is a resistor that terminates at the ground with that 22 uF cap. Does that make sense? Yes; makes sense - could go from 'other' pin 7 to ground. Might not be there but need to know.
if you have a resistor in parallel with that electrolytic cap, you have a belts-and-suspenders bias scheme <sigh>