I have a 64ish gibson scout ga17 rvt
I have had this thing since 1978 and it never worked right
I have spent the last couple nights going through it very carefully following the schematic, looking for dirty or bad connections
I got the thing working but still getting a lot of fuzz.
I have Isolated the cause to one the leads attached to one of the 6aq5 tubes
I saw some questionable solder joints on resistor, this resistor had a capacitor piggybacked on top of it,
I removed them and jacked em up so I cannot replace them
bottom line here is I need to identify the components and source replacementsI have a 64ish gibson scout ga17 rvt
I have had this thing since 1978 and it never worked right
I have spent the last couple nights going through it very carefully following the schematic, looking for dirty or bad connections
I got the thing working but still getting a lot of fuzz.
I have Isolated the cause to one the leads attached to one of the 6aq5 tubes
I saw some questionable solder joints on resistor, this resistor had a capacitor piggybacked on top of it,
I removed them and jacked em up so I cannot replace them
bottom line here is I need to identify the components and source replacements
I am way out on the end of my board here, I do not even consider myself a novice at electronics,
I have an understanding of theory but absolutely no practical experience
Any help would be appreciated.
I have attached a cartoon of the resistor I think it is a 270 Ohm resistor also a cartoon of the 20 MF Capacitor
Where Can I get replacements, I have no Clue
if anyone can point me to a supplier and a stock number it would be greatly appreciated
I have had this thing since 1978 and it never worked right
I have spent the last couple nights going through it very carefully following the schematic, looking for dirty or bad connections
I got the thing working but still getting a lot of fuzz.
I have Isolated the cause to one the leads attached to one of the 6aq5 tubes
I saw some questionable solder joints on resistor, this resistor had a capacitor piggybacked on top of it,
I removed them and jacked em up so I cannot replace them
bottom line here is I need to identify the components and source replacementsI have a 64ish gibson scout ga17 rvt
I have had this thing since 1978 and it never worked right
I have spent the last couple nights going through it very carefully following the schematic, looking for dirty or bad connections
I got the thing working but still getting a lot of fuzz.
I have Isolated the cause to one the leads attached to one of the 6aq5 tubes
I saw some questionable solder joints on resistor, this resistor had a capacitor piggybacked on top of it,
I removed them and jacked em up so I cannot replace them
bottom line here is I need to identify the components and source replacements
I am way out on the end of my board here, I do not even consider myself a novice at electronics,
I have an understanding of theory but absolutely no practical experience
Any help would be appreciated.
I have attached a cartoon of the resistor I think it is a 270 Ohm resistor also a cartoon of the 20 MF Capacitor
Where Can I get replacements, I have no Clue
if anyone can point me to a supplier and a stock number it would be greatly appreciated
Attachments
A Guitar Amplifier!
Perhaps someone in Instruments & Amps threads has actually fixed one of these.
This is the Valves / Tubes threads.
Perhaps someone in Instruments & Amps threads has actually fixed one of these.
This is the Valves / Tubes threads.
moved to instruments and amps.
You're right about the 270 ohms. The type of resistor is carbon comp, but those are hard to buy anymore. Use metal film or carbon film. Because of vacuum tube voltages, buy no smaller than 2 watt. 1/4 watt modern resistors are too short to hold off even 200 v.
20 mf 25 v caps have been replaced by 22 mf, usually 50 v is the lowest you can buy. The type of capacitor is aluminum electrolytic. I like to buy e-caps with a service life of 5000 hours or greater. When I bought e-caps at the TV parts store they would last for 8 or 10 years, only. Make sure installing that you get the + in the correct direction. Backwards e-caps blow their tops & short.
You didn't log a location. Farnell.com operates in 50 countries, but if you're in Canada, farnell ships from the US and a $20 UPS customs loan fee is required. Use digikey in Canada. In Europe, mouser RS or reichelt. Farnell & digikey, you can get the selector table to show you the hours service life. Mouser makes you download the datasheet & read it.
You must have a credit or debit card to use industrial distributors. Reloadable cards work if you don't have a bank account. You must order online, industrial distributors don't talk to amateurs on the phone. If you don't have a big enough order, they charge a handling fee. 100 resistors gets a lot more respect than 1. 10 capacitors the same way. Maybe a better soldering iron, pound of industrial 63/37 rosin core solder, a solder sucker bulb, spare fuses for this amp or your DVM, can bulk the order up to $25.
20 mf 25 v caps have been replaced by 22 mf, usually 50 v is the lowest you can buy. The type of capacitor is aluminum electrolytic. I like to buy e-caps with a service life of 5000 hours or greater. When I bought e-caps at the TV parts store they would last for 8 or 10 years, only. Make sure installing that you get the + in the correct direction. Backwards e-caps blow their tops & short.
You didn't log a location. Farnell.com operates in 50 countries, but if you're in Canada, farnell ships from the US and a $20 UPS customs loan fee is required. Use digikey in Canada. In Europe, mouser RS or reichelt. Farnell & digikey, you can get the selector table to show you the hours service life. Mouser makes you download the datasheet & read it.
You must have a credit or debit card to use industrial distributors. Reloadable cards work if you don't have a bank account. You must order online, industrial distributors don't talk to amateurs on the phone. If you don't have a big enough order, they charge a handling fee. 100 resistors gets a lot more respect than 1. 10 capacitors the same way. Maybe a better soldering iron, pound of industrial 63/37 rosin core solder, a solder sucker bulb, spare fuses for this amp or your DVM, can bulk the order up to $25.
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1W is fine especially running a low 300V. Tip Top Electronics in Canada. Time to replace the power electrolytic caps (22 uF) also since you are inside. If you are going to order parts you might as well get them all at one time. Would also be worth it putting 470 ohm 2W resistors inline with each screen on the 6AQ5's. Measure the rest of the resistors to see if any drifted. Replace the other e-caps on the cathodes, C1. I tried to find a gut shot of the chassis, no luck. Time to put in a three prong cord also. Get rid of C17 with that. Afterward you can consider the t-network after the first stage. Many people take it out, could just lift the ground and parallel a wire across it. Or if you like both ways to put a switch in to lift the ground and bypass it. A volume control with a push-pull dual switch would be a good reversible option if desired, but that is a consideration for a later date.
The 270 resistor was probably 2 Watt and it should be 5 Watts. (The voltage is almost 20V and 20V^2/270 = 1.5W, use double for good life is 3W, round up to next commercial size is 5W.)
A fuzzy schematic:
https://elektrotanya.com/PREVIEWS/63463243/23432455/gibson/gibson_ga-17rvt_scout_schematic.pdf_1.png
A fuzzy schematic:
https://elektrotanya.com/PREVIEWS/63463243/23432455/gibson/gibson_ga-17rvt_scout_schematic.pdf_1.png
Seems Gibson grounded one end of the heater supply. maybe add some 100 ohm 1 W resistors to the list just in case you need to modify the heater supply to float using the resistors as a midpoint common tied to ground or the cathode on the 6AQ5's. Noticed the cathode bypass electrolytic caps in the reverb, good to replace those also.
Thanks everyone for the help and suggestions, I managed to source the parts I needed installed them and actually got the amp working and sounding pretty good, there is a little bit of fuzz or distortion at high levels but that probably is to be expected.
If you have the 0.022uf cap from the power transformer and a resistor, could be 4.7- 10k or something, try them in series across the output transformer primary. Google 'conjunctive filter el84' and it might be something to try.
I think it´s just the amp reaching clipping, as every amp on Earth does.
Like OP stated:
Not a "defect" to be corrected but normal operation.
A 6AQ5 powered amplifier is not exactly muscular, speaker must not be too high efficiency either.
That said, a nice little amp for garage band rehearsal or *small* Club work, maybe Church work too.
Like OP stated:
Not a "defect" to be corrected but normal operation.
A 6AQ5 powered amplifier is not exactly muscular, speaker must not be too high efficiency either.
That said, a nice little amp for garage band rehearsal or *small* Club work, maybe Church work too.