Loved it! It's funny how sometimes we can overlook simple things and come back to it in the end. I don't know how many times I've done this myself with other things. Nice look at at an interesting amp. 👍
An outstanding display of perseverance, Stuart. It is one thing to overbuild an amp to handle the rigors of travel. It is completely another to overbuild one for the sake of overbuilding, and for no other reason. It was a brilliant persistence in deduction. I realize you have a conscience of foreboding regret to hand a customer a larger than normal repair fee. I must insist that although it may be part and parcel to occasionally incumber a learning curve to some units. Your time has value and I submit that you are due compensation for this exploratory surgery. Nevertheless, it is up to your discretion, and I hope you were paid for the trouble. This did make for an exciting episode. Well done. Cheers!
Hello Stuart. It's a brave man that takes on that repair. What a minefield. I tested out an old Carlsbro 200 watt Pa a few months ago. It had 720 volts on the B+. On the schematic it said, get ya gloves on, so out of the draw the gloves came. A really enjoyable video but please next time Stuart, get ya gloves on when you are probing the B+. Your'e a good bloke, we don't want to loose you.
6.3 Amp mains fuse! Reminds me of my Fender Super Twin Reverb from the late 70's. It uses a 6.25Amp fuse. It also has six power tubes (6L6's) and puts out 180Watts RMS, 395Watts Peak. I took the chassis out of the cabinet and built a separate head cabinet for it, so it's "easier" to move around. Ted Nugent supposedly used six Super Twin Reverb amps along with six Dual Showman speaker cabinets.
Stuart, you tested the gray ceramic fuse in circuit without lifting one end out of the fuse holder. This means that the heater-circuit fuse could be blown and yet if any tubes were still in place you would still read "continuity" (with some modest resistance) because of the heater-winding secondary of the power transformer and the parallel resistances of the tube heaters. (I presume this to be a heater circuit fuse because it has green wires going to it). I am posting this as a reminder to other newbie techs that fuses cannot always be checked for continuity in circuit ----- a heater circuit in particular will have not only the continuity created by the winding that feeds it but also by any tubes that are still plugged into the amplifier. Now, this particular amplifier probably has a separate winding for heating the preamp tubes (theyre still in place) compared to the output tubes, and the output tubes have been removed, but in many amplifiers all of the tubes together are fed by the same heater circuit secondary, and all those heaters are in parallel and therefore readable by the meter when you try to test the fuse for continuity, unless you pull all the tubes first. It's easier to just lift up one end of the fuse to measure its comtinuity!
I repaired a sound city 200w with 4x kt88's. Very heavy. I always start with a schematic to get an idea how it works. I spent too much time just prodding around and trying to work it out. Reduces repair time considerably
Hi Stewart. There are different ways to work on amps. I'm a 'schematic is the last resort' kind of guy. I can repair 95% of amps without a schematic.And if I have to fire up the scope, well....
This video serves as a great reminder to check the settings of all your switches and controls. You had no B+ to the outputs becauae it was in Standby mode; and then you had no audio because it was in a "mute" mode. PS, you could have fed the line-out into a bench-test amp to check if the preamp section was working or not. Anyway, note the Fender brand on the circuit board. Fender owns Sunn, and this is a sad reminder of Fender's decay, their downward slide into the Swiss Army knife, "everything-but-the-kitchen-sink" mindset of amplifier design.
@@stuartukguitarampguy5830 , Sunn amps (from the original company) used to be quite common on big stages here in the States in the early 70's ---- for instance, Leslie West of Mountain played "Mississippi Queen" on a Sunn amp, and IIRC Black Oak Arkansas used/endorsed them as well. They built PA amps and speaker systems as well as guitar and bass amps ---- but now you hardly ever see one, it's like they all vanished! PS, I myself had a solid-state Sunn "Coliseum" bass amp for a while around 1980, with a 2x18" speaker cabinet. It was quite a beast!
@@goodun2974 Interesting. My guess is that they all eventually failed and nobody wanted to take them on to repair. Class D is gradually taking over the high power amp scene. The worldwide valve shortage (which isn't going to get fixed) might be the final death knell for the valve guitar amp. It will take decades of course. I'm seeing a lot of younger musicians with a fancy modelling premp and a lightweight class D power amp. They don;t want to lug Fender Twins around anymore!
I don't think he actually had 6 valves to work with. He and/or the customer probably didn't want to shell out over $300 or perhaps much more $$$ for a half-dozen 6550's just to see if the amplifier worked or not. (PS, KT88's would have subbed for 6550's; same pinout, similar performance and specs).
I find it interesting you didn't look into the mismatched screen resister. all you really did was replace a blown fuse, that the customer told you was blown, and do some testing. Have you called the customer to see if the amp is still working?
I would hope someone would want that amp. Thanks for the video, always a treat.
Loved it! It's funny how sometimes we can overlook simple things and come back to it in the end. I don't know how many times I've done this myself with other things. Nice look at at an interesting amp. 👍
I always look forward to seeing your channel and am pleased you managed to get that monster going again.
Excellent work Stuart!
Thanks Dennis.
An outstanding display of perseverance, Stuart. It is one thing to overbuild an amp to handle the rigors of travel. It is completely another to overbuild one for the sake of overbuilding, and for no other reason. It was a brilliant persistence in deduction. I realize you have a conscience of foreboding regret to hand a customer a larger than normal repair fee. I must insist that although it may be part and parcel to occasionally incumber a learning curve to some units. Your time has value and I submit that you are due compensation for this exploratory surgery. Nevertheless, it is up to your discretion, and I hope you were paid for the trouble. This did make for an exciting episode. Well done. Cheers!
Thanks Alex I hope I don;t get another one!
Hello Stuart. It's a brave man that takes on that repair. What a minefield. I tested out an old Carlsbro 200 watt Pa a few months ago. It had 720 volts on the B+. On the schematic it said, get ya gloves on, so out of the draw the gloves came. A really enjoyable video but please next time Stuart, get ya gloves on when you are probing the B+. Your'e a good bloke, we don't want to loose you.
Ha Ha! Yes that 700V is lethal! I have a rubber mat I stand on plus rubber shoes.
Always cool to watch you Stuart 😎
Thanks!
6.3 Amp mains fuse! Reminds me of my Fender Super Twin Reverb from the late 70's. It uses a 6.25Amp fuse. It also has six power tubes (6L6's) and puts out 180Watts RMS, 395Watts Peak. I took the chassis out of the cabinet and built a separate head cabinet for it, so it's "easier" to move around. Ted Nugent supposedly used six Super Twin Reverb amps along with six Dual Showman speaker cabinets.
Stuart, you tested the gray ceramic fuse in circuit without lifting one end out of the fuse holder. This means that the heater-circuit fuse could be blown and yet if any tubes were still in place you would still read "continuity" (with some modest resistance) because of the heater-winding secondary of the power transformer and the parallel resistances of the tube heaters. (I presume this to be a heater circuit fuse because it has green wires going to it). I am posting this as a reminder to other newbie techs that fuses cannot always be checked for continuity in circuit ----- a heater circuit in particular will have not only the continuity created by the winding that feeds it but also by any tubes that are still plugged into the amplifier. Now, this particular amplifier probably has a separate winding for heating the preamp tubes (theyre still in place) compared to the output tubes, and the output tubes have been removed, but in many amplifiers all of the tubes together are fed by the same heater circuit secondary, and all those heaters are in parallel and therefore readable by the meter when you try to test the fuse for continuity, unless you pull all the tubes first. It's easier to just lift up one end of the fuse to measure its comtinuity!
This was very interesting!
Many thanks!
I repaired a sound city 200w with 4x kt88's. Very heavy. I always start with a schematic to get an idea how it works. I spent too much time just prodding around and trying to work it out. Reduces repair time considerably
Hi Stewart. There are different ways to work on amps. I'm a 'schematic is the last resort' kind of guy. I can repair 95% of amps without a schematic.And if I have to fire up the scope, well....
This video serves as a great reminder to check the settings of all your switches and controls. You had no B+ to the outputs becauae it was in Standby mode; and then you had no audio because it was in a "mute" mode. PS, you could have fed the line-out into a bench-test amp to check if the preamp section was working or not. Anyway, note the Fender brand on the circuit board. Fender owns Sunn, and this is a sad reminder of Fender's decay, their downward slide into the Swiss Army knife, "everything-but-the-kitchen-sink" mindset of amplifier design.
Yes beast of an amp and I hope never to se another!
@@stuartukguitarampguy5830 , Sunn amps (from the original company) used to be quite common on big stages here in the States in the early 70's ---- for instance, Leslie West of Mountain played "Mississippi Queen" on a Sunn amp, and IIRC Black Oak Arkansas used/endorsed them as well. They built PA amps and speaker systems as well as guitar and bass amps ---- but now you hardly ever see one, it's like they all vanished! PS, I myself had a solid-state Sunn "Coliseum" bass amp for a while around 1980, with a 2x18" speaker cabinet. It was quite a beast!
@@goodun2974 Interesting. My guess is that they all eventually failed and nobody wanted to take them on to repair. Class D is gradually taking over the high power amp scene.
The worldwide valve shortage (which isn't going to get fixed) might be the final death knell for the valve guitar amp. It will take decades of course. I'm seeing a lot of younger musicians with a fancy modelling premp and a lightweight class D power amp. They don;t want to lug Fender Twins around anymore!
Good job Stuart. I thought if anyone could fix it it would be you.
Cheers Zack.
So what was actually repaired and/or the cause of the blown fuses? Was the amp stable with all 6 power valves?
Yes surprisingly. Bad tube?
Hello Stuart! Great video!! Do you have news about that pot experiment?! Oo
Thanks Gabriel. Pot experiment edging up my 'to do' list!
U mentioned a variac is there one ud recommend for a beginner?
Get ta decently karge one to start with. They're not cheap though! I don't have a particula brand I can recommend..
What happened when you put all 6 power valves in…? Just curious. Great job of investigating a circuit backwards lol.
I don't think he actually had 6 valves to work with. He and/or the customer probably didn't want to shell out over $300 or perhaps much more $$$ for a half-dozen 6550's just to see if the amplifier worked or not. (PS, KT88's would have subbed for 6550's; same pinout, similar performance and specs).
@@goodun2974 Yes hat's exactly right. In the end I don;t think the customer actually used/restored this amp to its cab.
I find it interesting you didn't look into the mismatched screen resister. all you really did was replace a blown fuse, that the customer told you was blown, and do some testing. Have you called the customer to see if the amp is still working?
Yes the amp worked fine from then on.
Glad to hear it, and Merry Christmas@@stuartukguitarampguy5830
Ahaha! Just touch that and your finished !!
Yes super scary!
What happened to Fender?...cheap components laid out horribly...It seems Fender couldn't care less about it's customers or their amp techs
Yes gradul downhilll for decades. See my video on the Bluesbreaker 15!