The Amp Garage

I finely had time to get back to this problem. I wanted to post this to help other uninformed hobby builders like me. So as a recap this was a 2013 183 build. I changed tubes to some SIE EL34s in 2002. I did not realize that those tubes cannot handle more than 450vdc on the plates. A tube failure oc...

Thank you, your advice solved (albeit unfavorably) my problem. My amp was producing approximately 1/2 the design voltages, because 1/2 of the windings are DOA. I took disconnected the secondaries and read the voltages, 1/2 of the secondaries read the proper voltage, the other 1/2 read -0- volts, con...

Tonight my ODS 183 copy blew an EL 34 power tube. Afterwards, I replaced the tube with a fresh one noting that the B+ voltages were low. So I pulled the power tubes and checked the voltages throughout the amp. All of them are low. For example, the B+ voltage "unload" (no power tubes) is 252 vdc. Eve...

Ok I changed all the coupling and tone caps out. Voltages before AND after remain very strange. Here are the voltages: Tube 1......2....3.....4......5..... 6....7.....8......9 V1 347...na...0...na....na.....347....na.....0....na V2 347...na...0...na....na.....351....347....0....na V3 345...0....0......

Thanks everyone. Okay I found a broken ground and the PI tube socket was trashed. I bolted down the turret board, repaired the ground & replaced the PI tube socket. Voltages in V1 & V2 are high. The only sound I get is when I touch the phase inverter HV I get the usual crackle. I'm going to check th...

So I bought an amp that is a copy of a Matchless Lightning. It’s a 2 el84, 3 12ax7’ , treble bass and master volume, amp. When I fire it up I get no sound from my guitar. Instead I get a prominent 60 cycle hum. Changing the volume makes no difference. It stops when I pull the phase inverter. It does...

Found the problem, but only after running every test known to the internet and getting completely frustrated. One Winged C EL34 tube was internally shorted but my tube tester read it as "good". Here is how I found the problem. Using a 45 watt light bulb as a current limiter, I inserted each tube, on...

Awesome help everyone. One additional thing I noticed. Before I realized the H/T fuse was blown & the center tap was open I apparently overheated, but not to the point it opened up, the 3.9K resistor on the rectifier board. I replaced the 3.9k resistor and it's got me focused on the rectifier diode ...

Several (maybe 5-6) years ago, with much help from members of this forum, I built a 183. I have been using it regularly since. Yesterday, when playing, sound dropped out, came back & then the 1 amp B+ slow blow B+ fuse failed. This fuse is installed on the center to ground, like a Marshall 100. I ha...

Thanks for everyone's help. I figured out my problem. Here are the answers to Gil's questions: The switch is a DP3T (on-on-on) switch. Down - Bright on Clean engaged - the 120pf and 220pf are completely bypassed. (See below regarding the errand "red" wire from the switch to the volume pot lug.) Midd...

Okay I installed the bright on clean mod as drawn by Gil. In doing so I modified the bright switch so that each position of a 2d3p switch selects either a 120pf, 220pf or no bright cap. I installed the high pass filter on the OD relay board using 220K/470pf values. My question is ... why is the volu...

I'm generally a couple of years behind, sorry for the late post. I just bought a KAP and am finding it to be pretty amazing. I'm a tube amp snob, hobby builder since 2002 and have 45 years playing experience. Paired with a Yamaha DXR10 it sounds just like my 102 and my 183 clone. I'm looking for oth...

Thanks Tom. I highly recommend a current limiter as Tom suggested. I used one for this amp which is probably why I didn't blow up something. After all the mistakes I only fried one of my test 6v6's (an old 90's EH). An AB763 amp was much harder than I expected. My next project is a SSS 150w and I di...

Solution found, I forgot to make the bias filter cap to ground connection under the bias board.

Everything but the vibrato is working fine. I figured I'd have some troubleshooting on the vibrato since this is my first vibrato amp.

Thanks to everyone for the help.
Les

Martin,
As always your analysis is extremely helpful. I couldn't figure out how the bias circuit was even in the mix either. Sounds like at least one of my problems are in the bias circuit - but not because of my dumb mistake.
I a really appreciate your help.
Les