Menu

Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Messages - g1

#1
It is very common for the FM212 (and 65) to develop problems with the differential stage of the power amp (Q9 and Q10), which needs to be well balanced.  That could very well be the cause of your distortion issue, but even if not, it still needs to be dealt with.
Check R83,84,85,86 and replace any that are out of spec.
Replace Q9 and Q10.  This may be tricky as they are no longer made and there will be a lot of fakes available.  Try to get them from a reputable electronic parts supplier, not from Amazon or China.  * edit:  looks like Audiolabs of Georgia has them and they are a legit supplier.
It may be better to find a modern production sub for the 2SC2362K.
#2
Amplifier Discussion / Re: Acoustic 134 reverb
March 23, 2024, 08:09:02 PM
Yes, either will be close enough.  Looks like 8EB2C1A is available.
#3
Amplifier Discussion / Re: Acoustic 134 reverb
March 22, 2024, 06:46:49 PM
Quote from: Pete on March 22, 2024, 05:19:52 PMSooo ... the 4EB2C1B is an interesting suggestion. Can this be mounted either way? – Open side up or open side down?

I don't think they are all that fussy about it, I have seen manufacturers using tanks 'upside down' to what they are supposed to be.  Maybe when they get old and saggy they might start to bottom out.
But if the correct one is available, you might as well get that.
Studio Sound Electronics seems to have them all, including the 4FB series which would be an even better impedance match.  And they have them available in several decay times.
#4
Amplifier Discussion / Re: Acoustic 134 reverb
March 22, 2024, 01:17:02 PM
This listing shows a Gibbs 2 spring unit with about 200 ohms DC resistance at each end.  That would put it in the 4EB or 4FB range of tanks, I think a 4EB2C1B should work.

https://reverb.com/item/51673468-acoustic-control-corp-260-150-136-amplifier-gibbs-hammond-reverb-tank-unit-1969
#5
Amplifier Discussion / Re: Acoustic 134 reverb
March 22, 2024, 11:58:15 AM
Service manual attached.
This one is solid state so I don't think either of those tanks would be correct, but it is possible.
Reverb circuit shown on pdf pg.17
Drive is taken through cap C205 from a 40408 transistor.  Return into a MPSA05.
#6
Amplifier Discussion / Re: Watts vs Volume (db)
March 20, 2024, 08:39:30 PM
Quote from: JonnyDeth on March 20, 2024, 02:56:58 PMWell, looks like I wasted all that time going to college for electrical engineering, thanks for the clarification  ::)
If you can't apply it, I guess you did.
Amplifiers are rated into resistive loads to take reactive power out of the equation. 
Note that I specified amplifiers in my earlier comment to exclude what you said about speakers.

When one walks into a new room, it's best not to have the flamethrower on and start out with the idea that everyone else has it wrong.
#7
Amplifier Discussion / Re: Watts vs Volume (db)
March 20, 2024, 01:41:58 PM
Amplifiers are rated RMS into a resistive load, so VAR is not a factor at the amp side of things.
#8
Yes, sine wave is AC.
Normally we call it a 'signal generator' but it is also an AC voltage generator.  Amplitude and frequency are adjustable.
Function generators may also have other kinds of waveforms like triangle or square, which are alternating but not 'pure' AC.  Pure AC is sine.
#9
How are you going to get both wet and dry outs from the Orange?
#10
The T4 voltages indicate either T3 is bad and not letting T4 turn on fully, T4 is bad, or something is wrong elsewhere in it's string (shown in red).

You cannot view this attachment.

#11
Tubes and Hybrids / Re: Tube Amp Trouble
March 18, 2024, 08:14:04 PM
Sometimes certain ones don't light up as much as others.  But that one picture in the dark, it doesn't look like they are lit at all.  You could feel them to confirm. (just the preamp tubes, power tubes or rectifier tube will burn you)

The red and purple wires at the sockets are the heater wires.  Looks like they are all connected.  You can swap some preamp tubes around to find out if maybe the tubes themselves are bad.  Make note of where the 12AT7 belongs, but it can be swapped around for test purposes.

Once you have read up on safety for working in tube amps, you can measure those heater voltages at the tube sockets.  Should be about 6VAC with one probe to red and other probe to purple.
#12
Assuming that the T12 collector voltage TV mentioned is just a typo, T4 voltages do not seem right.  E-B voltage indicates it should be turned on, but collector voltage is not pulling down.
#13
Check that T7 and T8 and their diodes are ok. Check all 4 of the 0R33 5W resistors.
Power up on the bulb with no load connected.
Measure DC volts at e,b,c, of T4, T6, T9, T12.
#14
Service manual attached.
Sounds like 'Lo' input is the higher gain circuit (meant for lower output pickups) which is opposite to the usual arrangement.
#15
What is the wattage of your bulb?
I doubt that the 33VDC at the output was when speaker connected as that would be over 130 watts and your speaker would surely be toast.

Never try to power anything up on a limiter bulb while a load is connected to the amp.
Power up with no load.  Then, if no DC is present on the output, connect load while unit turned on.
Many amps will not power up properly on a bulb with a load connected.