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Messages - g1

Pages: [1] 2 3 ... 38
1
I have a feeling you are going low enough now with that resistor that it is affecting the bias of V1b (because it is in parallel with the 1K5 cathode resistor).
So it may be that what you are hearing is the change in V1b bias, rather than the change in NFB.
You can check this by measuring the DC voltage at V1b pin8.
With no signal, if the DC changes for the different switch positions, the bias change may be what you are noticing.
Ideally, the NFB should not affect the DC conditions of V1b.
If you really wanted to do a definitive test, you would then open the NFB loop, and put the resistors directly in parallel with the 1K5 cathode resistor, then compare the audible result.

2
Your meter readings sound about right.
You will always have R7 there, and it is basically in parallel with R15 because of the low resistance of the OT secondary.
Feedback can be very subtle and hard to notice.
Try open loop (no R15 installed), compared to a lower value like 5K for R15.
You should notice some difference, at least a bit of volume drop with a 5K for R15.  All other values between 5K and open, will be even less noticeable.

Also, with 5K installed for R15, it should read around 1K with your meter. (5K paralleled with 1K5)

3
The Newcomer's Forum / Re: Amp repair?!
« on: January 25, 2019, 03:13:48 PM »
Reading the heater voltage without the tubes installed is in this case not much help.
You need to check with the tubes installed.
Post your results.

4
The Newcomer's Forum / Re: Fender bass cab questions
« on: January 17, 2019, 02:31:39 PM »
The two 10's are wired in series.  So that part is simple addition, if they are 8 ohms each then the two of them in series is 16ohms.
Now you have 16ohms wired in parallel with 8ohms (the 18).
The equation for parallel is product over sum.  So (16x8) divided by (16+8)

Maybe your meter is reading high, disconnect one of the speakers and measure it by itself to get an idea of what your meter reads for an 8 ohm speaker.  Also, DC resistance readings on a meter are usually lower than the impedance rating.  So for a calculated 5.33ohm impedance, we expect the meter to read a little less.
Also note what your meter reads with the probes shorted together.  This should be zero, if it is 1 or 2 ohms or something, you must subtract that from your measurements.

5
The Newcomer's Forum / Re: Gear Suggestions
« on: January 15, 2019, 01:53:52 PM »
Have a look at the Aneng 8002 meter.  You won't find similar features and specs for that price anywhere else.

https://makeradvisor.com/aneng-an8002-an8008-multimeter-review/

6
Preamps and Effects / Re: Aion lab series l5
« on: January 15, 2019, 01:45:21 PM »
C37 in the IC11 circuitry I guess?

7
The Newcomer's Forum / Re: Update on Londoner L100A amp
« on: January 08, 2019, 02:32:16 PM »
You don't need a 6A switch, you need a switch rated 6A or more.
If the 15A will fit, use it.
If not, post some pics and measurements (bushing diameter), I'm sure there are switches available that will work.

8
The Newcomer's Forum / Re: Update on Londoner L100A amp
« on: January 06, 2019, 04:05:36 PM »
Those are power resistors (1ohm, 5watt).  They are shown at the emitters of the power transistors in the 100S schematic.
If they measure 1 ohm or less with your meter, they are probably fine.
The pot looks like it says 'lin' on it, which would be linear.

9
The Newcomer's Forum / Re: Splice output cables of matched speakers?
« on: December 29, 2018, 09:21:22 PM »
I wouldn't worry about the speaker power handling thing.  You are better off with speakers that can handle more power than the amp can deliver.
It would take an extremely inefficient speaker to cause you to turn up so much that you would damage the amp.  And most amps that did not have protection against that would probably sound so horribly clipped you would turn the volume down anyway.
Does the amp have reverb?  Sometimes a reverb tank will ring like that constant tone you are hearing.

10
The Newcomer's Forum / Re: Carlsbro GLX100 footswitch query
« on: December 29, 2018, 09:16:32 PM »
It came with an aftermarket footswitch for the and I believe the second channel, but not the other (optional) one. This is wired via a 4 pin DIN plug and covers crunch and reverb (see image below).
You have one footswitch with a 4pin DIN?
Does it control 3 functions?  Look at the labeling on the back.  Each jack controls 3 functions. 4th pin on each will be common/ground.  Neither jack says 'reverb'.
If you have 1 footswitch with DIN, plug it into the other jack and see what it does.
I would think they would both be wired up the same.

11
Amplifier Discussion / Re: HH IC100L schematic anyone?
« on: December 11, 2018, 12:00:22 PM »
I have only seen for the IC100 :  https://www.ssguitar.com/index.php?action=dlattach;topic=4500.0;attach=8135;image
For the 'L' version, I think you would have to buy it from maj electronics.

12
Amplifier Discussion / Re: Peavey Filter Caps
« on: December 03, 2018, 12:32:47 PM »
Edit : just when I thought things couldn't get any stranger, the preamp power supply pin now reads 43 volts. The resistor reads the same on both sides, after a new reading.  The audio pin reads 1.5 volts

:loco
If these readings are after mounting the board with the screws, that is probably why, it was not grounding before with the board lifted.

13
Amplifier Discussion / Re: Peavey Filter Caps
« on: December 02, 2018, 08:50:54 PM »
Also, in one of the pictures you can see through the board that there are ground traces that rely on the mounting screws to connect the ground to the chassis.  If the boards are not mounted with the screws, they probably will not work right.

14
Amplifier Discussion / Re: Peavey Filter Caps
« on: December 02, 2018, 08:48:17 PM »
Not sure where the naming of that pin as 'pa' is coming from?  Maybe it is marked on the board like that?
Anyway, I think it would be better to call it the 'preamp power supply' pin to avoid confusion.

So there is 0V coming out of the power supply/power amp board at the pin that feeds the preamp?
We need to find the correct power amp schematic for this amp.
There is probably a resistor that knocks down the main +V supply a bit before it gets sent to the preamp.

15
Amplifier Discussion / Re: Peavey Standard 260 Filter Caps (starting over )
« on: December 02, 2018, 08:42:04 PM »
Thanks for your understanding.  Some of us cranky old timers get confused easily.  ;)
Some of the info is always generic troubleshooting so it is best to leave it up unless you are the only one who has posted in the thread.
On the upside, I don't think anyone who is not a moderator should be able to nuke an entire thread, so you have helped identify a flaw in the forum software.

Discussion of this amp is continuing here:
https://www.ssguitar.com/index.php?topic=4518.15

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