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

Topics - Saransk

#1
Amplifier Discussion / Gibson GSS100 Noise and Pop Issues
February 15, 2022, 12:04:43 PM
I have a GSS100 that has had a complete cap and resistor update
Overall it works fine but has a couple of issues.
1 - Persistent hum.  May be just part of the design after I added a 3 prong AC cord.  Worse with Reverb turned up
I was thinking of adding isolated Input jacks and having a dedicated signal ground.
2 - "spitting" noise - random from the system.  No specific control or cause. Appears to be from the power amp since it occurs with either pre-amp chain.  The main Power Supply caps are new as are the ones
3 - Pops - loud., But it seems to be only with the "Rock - n - Roll" switch in the Off position.  Turning the Tremolo knob from Vibrato to Tremolo creates a very large pop.  Turning the amp off/on creates a typical "solid-state" pop.  But none of this occurs if the RnR switch is On.  It seems like there is a ground issue or "floating" voltage when the Vibrato Board is cut out of the signal path.
I've attached the schematics of the affected boards - I have the "B" model set.
Any ideas would be helpful.
#2
Amplifier Discussion / Hum increases with 3-prong cord
December 03, 2021, 11:24:59 PM
It may be coincidental but a couple of the restored guitar amps I've done seemed to have an issue with running a 3-wire AC cord with ground and removing the polarity switch circuit.
The latest is a Gibson GSS100 head that has a more pronounced hum after a cord and capacitor replacement.
I've had the same issue with a Vox Berkeley 3 head and a Fender 1st generation solid state Deluxe Reverb
The amps have the same type of transformer driven "totem pole" output circuit. Could it be that this type has an issue with the hard chassis ground with the 3-wire AC cord?

A very frustrating issue as I haven't added/removed any of the circuit grounds, the inter-board wiring was the same.
Thanks
Michael
#3
I have a really nice, working, 2nd version Sears/Silvertone 200BLX head.
It has been upgraded once (caps) and sounds great
This is the later version with a more modern power amp - no driver transformer - looks like a Hafler or Kustom amp

The service manual lists all the parts with a Sears part number, no a problem with the passive parts, but no idea what the original devices were.  The driver transistors appear to be TIP devices (220 case) and not original.

Any place to find a cross reference for Sears transistor part numbers?
Thanks
Michae