First Post - Help with 18 Watt Build

[jobewan]

Hi All,

I am really glad I found this board. I have completed a build of the Tube Depot 18 Watt kit. All went well with the turn on and testing, until I connected my guitar to the amp. I have a function generator that let me inject a signal (800 Hz at 150 mV). That signal makes it out to the speaker without a problem. It responds to volume control changes and to the Trem circuit. At least it sounds like it does. However when I plug my Strat in I get this horrid blatty highly compressed god awful sound. You know the garbled noise that you can get when you shut off your amp and the tubes are going down? Thats how it sounds all the time. The good news (or bad news, if you are my wife...) is that this noise responds to volume changes.

So I have a bunch of equipment (I love tools...), but I am very new to electronics. I am hyper cautious - I know there are some hefty charges in those caps.

The most significant problem I find when testing is that the voltage across the power resistor is too high. The manual lists 11 volts expected at turret T55, which is the 5 watt power resistor, I get 22 volts there. In addition, when reading the voltage at the can capacitor in the power tube testing section, the values are in spec, but just barely. I am reading ~+310 volts on the B side (+345 expected), and +282 volts on the A side (+320 volts expected). The manual allows up to a 15% variance for the power tube section. Those numbers are just within spec..

Can anyone out there with some stick time on this build give me an idea what to look at? I would be very appreciative. I am stuck.

Thanks

Joe

[Studiocat13!]

Wish I could help you Joe but I am currently working in the same circuit so once completed I may have a better idea of what to look for. Did you reach out the Tube Depot for support ? The other thing to do is just really go back through the entire schematic and layout and be sure you didn't wire something wrong which is very easy to do. I usually triple check everything I am doing during the build and compare the layout and instructions against the schematic just to ensure I know what I'm doing and why I'm doing it. I know its tedious but you may very well find what is causing the issue...
Good luck and keep me posted !

[JMPGuitars]

I am really glad I found this board. I have completed a build of the Tube Depot 18 Watt kit.

Hi Joe,

For troubleshooting, here's where you start:

1. Post the schematic and layout you used.
2. Get a highlighter.
3. Use it.

Even if you think you already verified your build, print the schematic of your build, and verify every component value and connection, highlight each piece after verifying. Since you used the Tube Depot kit, I would suggest also verifying that the schematic and layout match as well.

Once you've done that, use the voltage chart to share all of your voltages here. Also post some high resolution photos of your build. You can use the gallery on the menu on the left for that if you'd like.

Thanks,
Josh

[geoff 1965]

Hey Joe!
good advice from Josh,here's the schematic and layout for everyone to look at. you will have to tell us any mods you have i.e. is it just ez81 rectified or do you have the diodes as well? also does it have the B+ choke or the 2K2/3W resistor?

british18w_schematic_v5.pdf

British_18W_layout_v20.pdf

[jobewan]

Hey Folks - thank you so much for the help - I got pulled away by work, but hopefully I can get back to this now.

I will do the schematic trace with the highlighter. I did tread that thread before I posted. That is great advice.

Geoff - I have built the amp without any mods. THe rectifier is the straight ez81, and I have the 22K, 3 watt resistor across the can cap terminals. FWIW - the two docs you posted are the 2 docs I am living by - they are the ones that came with the amp instructions, and I have downloaded the current ones off the Tube Depot site and have been using them to troubleshoot.

I just received a new EZ81 and will see if that helps. I also have a buddy who is a little more versed in this that I am, and he is going to come over Friday night and help TS.

BTW - I am absolutely loving doing this - it is a fantastic hobby. I have turned a room we have into my lab, and I have a great bench and went nuts buying test equipment (we are DINKS, and I have a little bit of disposable income - bought the Rigol DS1054Z scope, and a Siglent function generator, and really nice SIglent DMM. I am cooking with gas, to quote a phrase I never quite understood.

I just made up an 8 Ohm 20 watt dummy load, and I plan on tracing the circuit out using an injected signal - we shall see... I have been watching Youtube videos on how to do all this stuff. I am careful as hell, and my wife is constantly looming to be sure I bleed caps etc.

Thanks again - very much appreciate the help. I will do the schematic highlighter trace asap.

JB

[geoff 1965]

hello Joe,
sounds like you've caught the "amp bug" like the rest of us! i finished my lite2 build well over a year ago but still can't resist tweaking and experimenting with it!
double check the value of the can capacitor resistor! it should be 2.2k not 22k,what voltage do you have to the OT primary "pin3" of the ez81?
noticed you are dropping 30 volts across the can cap,i have the can cap & 2.2K across and i've got 352V in and 331V after the resistor.

[JMPGuitars]

Geoff - I have built the amp without any mods. THe rectifier is the straight ez81, and I have the 22K, 3 watt resistor across the can cap terminals.

BTW - I am absolutely loving doing this - it is a fantastic hobby. I have turned a room we have into my lab, and I have a great bench and went nuts buying test equipment (we are DINKS, and I have a little bit of disposable income - bought the Rigol DS1054Z scope, and a Siglent function generator, and really nice SIglent DMM. I am cooking with gas, to quote a phrase I never quite understood.

I just made up an 8 Ohm 20 watt dummy load, and I plan on tracing the circuit out using an injected signal - we shall see... I have been watching Youtube videos on how to do all this stuff. I am careful as ****, and my wife is constantly looming to be sure I bleed caps etc.

First, I'm guessing for 22k 3w, it was a typo? 2.2k 3w, right?

I think it's great/hilarious that your wife is verifying that you're bleeding your resistors. While this is still a good practice, I think it's ridiculous that this build doesn't have a bleeder resistor on the cap can.

For anybody building this kit, I would add a permanent bleeder resistor by doing this: add a 220K 1W resistor from the cap can to ground. Take a look at the cap can on my drawing here: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf - the 220K resistor on the left side of the cap can is what you want to copy.

EDIT: one more important thing, don't use transformer mounts for anything but mounting transformers. Ground wires should always have their own holes. The IEC socket ground wire should be as close as possible to the socket, and not be shared with anything else.

Did you get the free upgrade code for your scope?

Thanks,
Josh