Ampeg SVT-CL LF Boost Switch issue

[nevetslab]

On this same Ampeg SVT-CL-Heritage Bass Amp, I've discovered after some digging, that the custom dual-stacked 4PDT + DPDT switch installed in the HF Boost/LF Boost switch location of the Preamp, it being PCB-Mounted switch, one of the two internal wiping contacts of the LF Boost Switch is missing the sliding element, so the LF Boost Function doesn't work. Went thru removing the three axial mounted ceramic caps (56pF, 470pF and 4.7nF) in order to measure them on my bridge, and had measured/verified the resistors in the circuit, so all the components were correct. No PCB issues found. But then not finding the presence of the one moving contact of the LF switch was very disturbing to find. You can't buy one of those from distribution. Custom Made switch, ordered in Qty from the mfgr by Ampeg all these years.

I have to wonder how it made it out of the factory with that defect?

Now have to find the solution. Brand new amp, so perhaps this is a Warranty issue. Wonder if cutting out the clear plastic garden hose harness coverings on the AC Power/Standby harness and the DC harness coverings and replacing with flexible Tech Flex that does withstand the hi temp in close proximity to the power tubes would be grounds for not honoring the warranty. All SVT-CL's I service gets that mod for ease of servicing the power tubes over time.

[mikeydee77]

In the UK yamaha spares are very good they seem to have all the parts though shipping is a bit slow. How is it in the US?

[nevetslab]

I'm about to find out. Not being a qualified Service Center for Ampeg (now owned by Yamaha), not sure if I can directly order the replacement part. As I believe the amplifier itself is nearly brand new, purchased by AuntieM Creative Consultants, Inc in Alhambra, CA, so it might be easier to obtain either the complete PCB assy or the Preamp assy, though it being a Heritage model, maybe not so. Black double sided PCB, and of course tiny solder pads used in the layout for the double-decker switch. I have a feeling that switch itself isn't an item that's inventoried here in California. Won't know much until I start the pursuit.



I suppose if I learn the lead-time is way out, I could probably order some 4PDT and DPDT single pushbuttons in that format and cobble the assembly to meet the mechanical specs of this custom switch so the vertical spacing matches. At present, my current PACE desoldering station's vacuum system is in need of service, not having sufficient vacuum to suck solder out of double-sided PCB's like this. Waiting for the older PACE SX230 coming in from nosaj which has a better vacuum system.

[g1]

In the worst case, is it possible to disassemble and replace the wiping slider in such a switch? If you have another of the same make it may be possible to use it for parts.
I know I have done similar but not sure about this exact model of switch.

[Delta362]

You might be able to order the switch from yamaha24x7.com, if you can find the part number. Otherwise, Studio Sound Electronics has them for a pretty penny.

https://www.studiosoundelectronics.com/switches.htm




Edit: Looks like Fliptops has them cheaper.
https://www.fliptops.net/catalog/p-1...vt-cl-and-more

[nevetslab]

I haven't attempted to uncouple the actuator on the lower switch, and then install one of the contacts from a similar switch. Yesterday, while having contacted the local Authorized Ampeg Service Center up the street Audio Design Services, Inc Burbank, CA, they are waiting for my client to forward their purchase invoice for the amp, as it is under warranty, and this firm is indicating they can provide the replacement switch assy at no charge. I've meanwhile ordered C & K F2UEE DPDT and F4UEE 4PDT push button switches to cobble a replacement switch to replace the defective one, just in case.

I hadn't thought to check Studio Sound Electronics to find that they list that custom switch. The cost of the switch doesn't surprise me, as it isn't a standard distribution item.

Either way, still need to get more vacuum in my Pace MBT 250/SX70 Desoldering System so I don't damage the solder pads of the smallish solder pads and blow out the plate-thru of the holes.

[nevetslab]

Now to aid in the removal of the defective switch, nosaj's older Pace SX230 Vacuum Pump desoldering station arrived today, so now digging thru it, finding the first limitation in the vacuum is the final fitting from the 3/8" threaded brass fitting to mate with the hose of the SX20 desoldering handle. In the process of reaming out the ID of the adapters to increase suction. looks much like the vacuum system I had in my first Pace Desoldering Station, with the base unit from APE PRS475. So, time to cobble two systems together for (time being) greater suction than I'm getting from their alternative vacuum system in the MBT series. Nothing is ever easy.

[Tom Phillips]

Now to aid in the removal of the defective switch...

This might be a good time ti use Chip Quik.

[nevetslab]

Actually, the surgery went well, now have more vacuum suction from the better Vacuum Pump Pace used to use, opened up the throat size of the final hose reduction fitting and not using any adapter (which restricts dia of the throat), and I have plenty of suction now. Tried it out using my SX70 Desoldering Iron on an old Aguilar DB750 Volume Pot, which was dual gang, plus a push-pull switch behind it. Sucked the solder out of that ok, aided with feeding fresh solder to get the 'juices' flowing. Had to use solder braid to remove the solder on the rear of the switch which had a wide support tab.

Also cleaned out the throat and dross chamber of the SX20 Desoldering handle, along with the throat of the tip holder/heater assy. Found my collection of SX20 tips, needing the 0.060" dia tips, and that likewise worked. Both using the pedal to run the motor. I'll tackle adapting the AC power control to turn the pump motor on/off from the SX70's handle-actuated button later when I have the time. And, when there's nothing else better to do, tear into the MBT250's suction motor system to see what I can do with it. Not sure if that has replacement parts to rebuild it, but I do have other PACE MBT units that could be cannibalized.

[nevetslab]

You might be able to order the switch from yamaha24x7.com, if you can find the part number. Otherwise, Studio Sound Electronics has them for a pretty penny.

https://www.studiosoundelectronics.com/switches.htm




Edit: Looks like Fliptops has them cheaper.
https://www.fliptops.net/catalog/p-1...vt-cl-and-more

My C & K DPDT and 4PDT switches arrived today. As the width of the switch terminals is only 0.015" thick, I'm sure there's more than enough clearance in the button openings in the front panel to accommodate a shift in the upper switch by that much, so just getting the height separation between the two switch bodies is the main criteria and cobbling this dual switch assembly together from those separate parts.

[nevetslab]

While waiting for my client to find the sales receipt on their Ampeg SVT-CL Heritage amp, they finally found it and sent copy to that Authorized Ampeg Service Center up the street from me (Audio Design Services, Inc Burbank, CA). Got an email from them advising me that I could now bring the amp up to them any time. ???!! Excuse me? Ain't bringing no amp to you. I need you to track down and send me the faulty switch assembly that you indicated you could do, provided this isn't a long lead time. I'll be curious to see if they CAN get the part in a timely fashion. If so, then I'll take them up on obtaining the part. Otherwise, now having parts to cobble with, I wonder which I'll choose? (repair now can be finished in a couple hours).

[nevetslab]

I gave up on Audio Design Services, Inc Burbank, CA to come thru with the replacement LF/HF Boost Switch assembly. So, having ordered and received C & K F2UEE and F4UEE DPDT and 4PDT switches, I found after unsoldering the faulty Ampeg-installed switch, the spacing between upper and lower switches was 0.494", and just sitting the F2UEE atop the F4UEE switch, I was within that window, so no fancy foot work to go thru to achieve the spacing. Checked it also with the switch buttons installed, and verified it was well within the window of the chassis opening. After removing the faulty switch, I also noted that the front pair of lower contacts of the 4PDT switch needed to be removed so pushing the LF Boost button didn't also turn on the HF Boost. So, had to open up the F4UEE Switch to extract those forward contacts. To extract the front switch contacts, there's a little plastic stop on the top of the housing of the switch that can be lifted up with a very tiny screwdriver blade (after you've removed the alternate-action bar held in place by the switch spring). Got those removed, then applied solder to the front switch terminals of the F4UEE switch and the PCB Terminals of the F2UEE switch and tack-soldered them together. Verified the results before soldering into the preamp PCB. Not quite the same as the factory-made long PCB terminals used to pass thru the 4PDT switch housing, but the thickness of those PCB terminals is only 0.020" thick, so scarcely matters there being that much shift of the upper switch body.





That solved the lack of LF Boost Function on the preamp.

Now, the actual reason this amp came to me was it was found to be weaker in output than other SVT-CL amps driving an 810 Bass cabinet. This is where the digging into what the real output power of Ampeg SVT-CL amps (and SVT-VR amps) was at clip. I have this restored working SVT-CL-Heritage amp running in the background here in the shop, and I see the SPL level of the Burst Pink Noise source only hitting 103dB where it is just starting to clip. Pushing it harder only yields distorted compression of the output, with very little increase in SPL on the B & K Analyzer I have sitting on the desk, about 20ft away from the Ampeg BXT-115HL4 15" bass speaker cabinet at the end of the shop. I was getting 105-106dB SPL out of the older SVT-CL amp that I just replaced power tubes on (installed fresh matched Sextet of J/J KT88 power tubes, along with new ECC82 drivers and ECC83S input stage tube in the power amp chassis.

I didn't try those new KT88 power tubes in this amp, but from what I had previously on that older SVT-CL, using 6550's to the new KT88's installed, I was getting near identical SPL readings at clip.

Won't know about the existing power tubes in this Heritage model until I swap power tubes. That's another $300+ for that exercise, and up to the owner on that one. At least I solved the faulty LF Boost Switch problem. Onward......

[x-pro]

To make the removal of multi-contact parts easier and faster,, you can use a fusible solder. For example, a Rosé alloy. After removing the part, this solder must be removed. The portion that will remain on the solder is very small and can be neglected when using conventional solder.
A high-vacuum device is not needed.

[nevetslab]

In removing the 12-contact switch assembly from the PCB, having restored and increased the vacuum suction of nosaj's vintage Pace SX230/SC20 desoldering station, I added a touch of lead-free solder at each solder pad to get the heat flowing, and that sucked the production solder out just great. I can't see I've ever heard of Rose alloy. In this operation, the part was already installed via flow solder system at Fender's factory, so ya gots ta use vacuum (or solder wick) to extract the original lead-free solder.

[x-pro]

Rosé alloy has a temperature of less than 100 degrees Celsius.