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Messages - Psabin8951

Just got back to this.
No fuses blown.
I've replaced the diodes and its definitely not just them.
Does anyone have a pic of what voltages lurk where on the mains transformer as it's not maked. I then can rule that out hopefully.
Thanks in advance
Tubes and Hybrids / JTM60 Combo rectified diodes fried
November 05, 2019, 04:15:27 PM
I have just been given a JTM60 combo.
Its HT rectified diodes D105,106,107,108 are all blown (literally!).
Obviously I can replace these but what would have caused this?
A friend has just got hold of an ENGL Fireball E625 60 watt amp head. Looks in good condition and works but...
When ultra gain switch is turned on there is a large amount of white noise with the guitar sound.
If the guitar is plugged into the effects return and level set to full effect then there is no noise just pure guitar.
Any thoughts on the cause? The seller told him it has had new valves but obviously that's not gospel!
Thanks for the fast reply.
I used a mica sheet plus grease.
Collector shows no connection to heatsink or chassis on meter.
There is continuity back to -V on C61 and DB1
Ok pinout issues resolved and TR10 now replaced.
TR readings now are:-

TR4 B 0.01v C 0.01v E 0.07v
TR5 B 3.33v C 0.01v E 3.73v
TR6 B 4.35v C 7.76v E 3.8v
TR7 B 8.21v C 0.58v E 3.47v
TR8 B 0.53v C 8.41v E 2.14v
TR9 B 0.2v   C 0.53v E 0.08v
TR10 B 0.08v C 0.02v E 1.42v
TR11 B 1.59v C 0.03 E 1.76v
TR12 B 1.54v C 1.55v E 1.76v

J M Fahey, only reason they were stated as being "ok" was they had been replaced with new components.
Anyway two discoveries now - yes TR10 is dead CE & EC both read 0.02 so that needs replacing. I have also noticed that for the emitters on TR11 & TR12 then one must be fitted the wrong way around. Turns out TR11 is wrong but is fitted as per silk screen which seems odd. Checking all other connections for BC212s apart from that one they fitted correctly which seems most strange. I will make those corrections and report back
Sorry G1. I tried to make my life easier by getting the wife to write voltages down as in probed components.
Obviously that didnt pan out! Anyway i've now redone them. Pinouts were taken from datasheets, my "helper" put some voltages in the wrong columns doh.

Right take 2:-

TR4 B 0.019v, C 0.75v, E 0.07v
TR5 B 2.93v, C 0.02v, E 3.25v
TR6 B 3.97v, C 6.86v, E 3.42v
TR7 B 6.86v, C 10.2v, E 7.19v
TR8 B 1.03v, C 7.18v, E 0.9v
TR9 B 0.89v, C 1.03v, E 0.76v
TR10 B 0.76v, C 0.02v, E 0.17v
TR11 B 0.35v, C 0.52v, E 0.03v
TR12 B 0.71v, C 0.85v, E 0.53v

Ok results are:-

TR4 B 0.2v, C 0.75v, E 0v
TR5 B 2.9v, C 0.2v, E 3.2v
TR6 B 3.9v, C 3.4v, E 6.79v
TR7 B 6.8v, C 1.02v, E 7.13v
TR8 B 0.89v, C 7.09v, E 1.03v
TR9 B 0.83v, C 1.03v, E 0.76v
TR10 B 0.17v, C 0.02v, E 0.76v
TR11 B 0.35v, C 0.52v, E0.03v
TR12 B 0.7v, C 0.53v, E 0.86v
So what now guys?
Correct, there is no load currently connected.
I haven't got a bulb limiter but can construct one fairly quickly.
Ok after a delay due to tonsilitis im back on this. TR4 - TR12 now checked. All ok except TR8 which has now been replaced.
Fuse instantly blowing now.
Any suggestions where to go from here?
I have a poorly Marshall 808 combo come my way.
It was blowing the internal fuse when received and by isolating the circuit I know the +15v and -15v areas of the circuit are ok as is the tube heater portion which leaves the power amp stage. With R84, 85 and TR8 removed from the circuit it powers up fine.
With R84 reintroduced again it powers up fine.
With R85 added too, that resistor severly overheats but doesnt blow fuse.
If TR9 is out of circuit R85 doesnt overheat.
With R85 back out and TR8 refitted the fuse blows.
Can anyone point me to what is likely to be the cause?
I have attached a pic of the circuit in question
I've just had a Blackstar Series One 45 Combo come to me with no output.
Upon inspection there are two resistors totally burnt out - R3 on the EL34 power tube board and R6 on the ECC83 board.
Does anyone know the values of these components and or have a schematic please?
Amplifier Discussion / Re: Vintage Roland Cube-60 Reverb
September 12, 2017, 09:04:57 AM
Bad choice of wording perhaps Enzo but input is sub 1 ohm and output is 180 ohm. This situation has also been proven by temporarily fitting another reverb to the PCB sockets which results in a working system. I just want to be sure that the reverb tank I purchase has the right impedances.
Amplifier Discussion / Vintage Roland Cube-60 Reverb
September 12, 2017, 02:27:58 AM
I have an old cream coloured Roland Cube-60 which came to me with reverb issues.
Initially it had no drive going to the spring tank input, that was due to a pin sheared at pcb level on the driver ic. With that sorted there is sound going in but nothing coming out unless you twang the springs. So I'm guessing a new tank is the best bet but does anyone know what spec I need ie input/output impedance and delay length?