replaced the switch on my PM7

What? C'mon don't make fun, that was a mild pain in the ass. You can see little bastard tantalizingly exposed by lifting up the pedal cover/battery access...only to have to remove as many layers as the movement of a swiss pocket watch to get at the actual switch itself. I'm lightly proud of this small victory.

Ampeg RB-115:



This thing must have been a store return. Not sure why it didn't make its way back to Ampeg for warranty replacement, but their loss, my gain. Arrived in its original box with manuals and hang tags. Looks brand new.

Flying blind, as Ampeg said this thing was too new to the market and they wouldn't send me a schematic.

No output, so I started working my way back from the speaker. Found that the Class D driver IC (IRS2092) was stuck in reset at boot. Verified that the output MOSFETs weren't shorted and all the rails looked good, so it should have booted. I replaced the IC (had to steal it from a cheap Class D amplifier kit that I found online, as digikey and mouser didn't have stock of the IC itself), and it still didn't boot, but the behavior was different. The CSD pin on the IC was getting stuck at GND, where it should have transitioned from -5 V to GND to + 5V. Something was holding it in standby. When I disconnected the preamp circuit header, it booted normally, so I started probing the preamp board and flexing it, looking for intermittent issues. Found that when I flexed the board at the headphone/aux-in socket, it booted normally.
Reading the manual, it is supposed to mute the output when headphones are inserted. I saw that the MUTE pin on the preamp to poweramp header was pulled high until I flexed the board. The headphone socket has a switch on the tip terminal that indicates when the jack is inserted. It wasn't making contact until I flexed the board enough to tweak the internal terminals enough. Took off the socket shielding and bent the terminal until it made contact, and everything is functioning now.

I still think there was something wrong with the IRS2092, but kinda wished I had started at the preamp and worked forward before tearing into it and replacing SMT components.

Nate Dort wrote: Ampeg RB-115:

This thing must have been a store return. Not sure why it didn't make its way back to Ampeg for warranty replacement, but their loss, my gain. Arrived in its original box with manuals and hang tags. Looks brand new.

Flying blind, as Ampeg said this thing was too new to the market and they wouldn't send me a schematic.

No output, so I started working my way back from the speaker. Found that the Class D driver IC (IRS2092) was stuck in reset at boot. Verified that the output MOSFETs weren't shorted and all the rails looked good, so it should have booted. I replaced the IC (had to steal it from a cheap Class D amplifier kit that I found online, as digikey and mouser didn't have stock of the IC itself), and it still didn't boot, but the behavior was different. The CSD pin on the IC was getting stuck at GND, where it should have transitioned from -5 V to GND to + 5V. Something was holding it in standby. When I disconnected the preamp circuit header, it booted normally, so I started probing the preamp board and flexing it, looking for intermittent issues. Found that when I flexed the board at the headphone/aux-in socket, it booted normally.
Reading the manual, it is supposed to mute the output when headphones are inserted. I saw that the MUTE pin on the preamp to poweramp header was pulled high until I flexed the board. The headphone socket has a switch on the tip terminal that indicates when the jack is inserted. It wasn't making contact until I flexed the board enough to tweak the internal terminals enough. Took off the socket shielding and bent the terminal until it made contact, and everything is functioning now.

I still think there was something wrong with the IRS2092, but kinda wished I had started at the preamp and worked forward before tearing into it and replacing SMT components.

That's funny. It started off sounding complicated, but it ended up being the familiar old- an intermittent switching TS or TRS socket?

VHT D-fifty:


It's a Dumble ODS clone. Hand-wired (in China) on turret board. Advertised as not powering on. They were correct. Bought it from a music store that claimed it was a brand-new customer return. Date code is from September 2021. Not sure why the didn't get an RMA for it and get it replaced by VHT. ASCIISHRUG

Traced the mains to an open primary side on the power transformer. Even peeled back the tape on the transformer bobbin to expose the joints where the hookup wires are soldered to the windings. Still open. I was rolling the dice and hoping it was something easy to fix, but this is pretty much the worst case scenario, cost-wise.
The silkscreen on the JJ output tubes is discolored, so maybe they were redplating or something. Need to throw them on the tube tester.

I emailed VHT about specs for the PT so I could source a replacement, and they responded within hours and sent me the full schematic with voltages. That was unexpected. This is the first they've heard of a PT with an open primary so they seem curious. I gave them the backstory. Waiting to hear back if they've got a replacement. Fingers crossed that they warranty the thing and just send me a new one.

Its kinda rad that they're making an amp of what seems like pretty good build quality for that price (~$1K new). Dumbles are kinda whatever to me but, per discussion in the Gear You Hate thread, would be very cool to see them making plexi or BF bassman clones of the same quality and price point.

Nate Dort wrote: Thu Oct 27, 2022 9:58 am Whoops, bought a broken Earth G2000.

This arrived today. Might be the dirtiest amplifier I've ever worked on. Instant smell of tobacco smoke when I removed the bubble wrap.

Transformers and all of the jacks are covered in surface rust. It came from Florida, so I'm not surprised.
Preamp tubes are all Mullards, labeled IEC, which was the contract house that built these things for Earth.
Three of the 6L6GC output tubes are USA made, most likely GEs based on the text and short bottles. One is a tall skinny bottle, branded Raytheon, made in England (probably Mullard). Haven't tested any of the tubes yet.

I do like that the bottom panel of the cabinet comes off with four screws, which removes the reverb tank and exposes the circuit. Dated 1/17/73.


Gonna start with a full recap. Some of them are visibly leaking electrolyte. Transformers are shedding enough rust particles that I probably need to pull them off and hit them with a wire wheel and a rattle can of paint. All the RCA and 1/4" jacks need to be replaced also. Too much rust.

Two of the knob set-screws are stuck. Might have to drill those out and replace with something new. I'm trying penetrating fluid for now. The other knobs are going into the ultrasonic bath.

Nate Dort wrote: Fri Oct 28, 2022 8:12 pm VHT D-fifty:
Fingers crossed that they warranty the thing and just send me a new one.

No dice, since I didn't buy it new at full retail price.

They said 2 to 3 months for a replacement PT. Then they recommended I get one for a hot rod Deville, but that one doesn't have the 60V bias winding or an aux winding to generate the DC voltage for the switching relays.

Hammond 290DX looks like it should work if I swap the 12V relays to 5V.

VHT D-fifty (cont):

Got this buttoned up with the Hammond 290DX in there. Had to make a couple of mods to get it to work (convert from bridge rectifier to full-wave, change the relays from 12V to 5V coils and replace the 7812 with a 7805 regulator).

At least one of the output tubes was shorted, which is probably what took out the PT. Tested OK on my tube tester though. I don't know.

Swapped the 6L6GCs for EL34s, because I had a pair on hand and that’s what the original used. Made a couple of other minor signal path mods to more closely match the original schematic. Removed LNFB on V1b, bypassed a coupling cap going into the OD circuit that wasn't on the original. Sounds pretty good. Less fizzy than the online demos led me to believe. I've got a couple more easy mods I'm going to try.

Earth G2000 (cont.):

Found a couple issues once I started recapping:

1) First B+ dropping resistor was blown open.



2) The last 20uF B+ filtering cap (point E) wasn't even connected on the ground side. The lead was inserted into the tag, but never got soldered. Must have left the factory that way.


Schematic:


Work performed so far:

• Cleaned all the gunk off the chassis with denatured water, isopropyl alcohol, contact cleaner, and finally some engine degreaser. Had to use a green scrubbing pad to get most of it off.

• Cleaned the front and back panels with a magic eraser. May hit them with some Novus polish as well.

• Cleaned the cabinet upholstery and recessed handles.

• Cleaned the knobs in the ultrasonic cleaner.

• All electrolytic caps replaced. Had to drill a new hole for the multi-section cap, as I used a JJ cap with a clamp.

• Replaced all the rusted 1/4" jack hardware. Jacks themselves were fine.

• Removed all of the RCA connectors and replaced with 1/4". Went to 1/4" TRS for the footswitch jack so I can use an off-the-shelf 2-button footswitch.

• Replaced the B+ dropping resistors.

• Cleaned/lubed all the tube sockets.

• Cleaned/lubed all the pots.

• Repaired a broken output tube retainer.

• Replaced the blown fuse.

Need to button up a few minor things before I can bring it online.

Nate Dort wrote: Tue Nov 08, 2022 7:38 am Earth G2000 (cont.):
2) The last 20uF B+ filtering cap (point E) wasn't even connected on the ground side. The lead was inserted into the tag, but never got soldered. Must have left the factory that way.

Just read up on the barely-there history of Earth and yeah this does not surprise me in the least. Doesn't sound like as a company they did much of anything interesting beyond a strange attempt at a Marshall amp. This seems especially in later years when they were straight-up copying Peavey of all things - which is utterly bizarre to me. That's not to knock Peavey, just seems like if you were going to do a cheaper knock-off, you'd pick something a little more expensive or inaccessible than Peavey. I guess they were very popular and so that's why they ended up as the target...? Idk. Baffling.