Micro Bassman LTP issues

[D'tar]

any luck chop sticking the circuit? do any of the pots influence the motorboating/noise?

 

[Camdenharr]

any luck chop sticking the circuit? do any of the pots influence the motorboating/noise?

Okay so unexpected success… I was doing some cleanup on the amp and all of a sudden it roared to life and is working with no oscillation… I checked it left, right, upside down, and sideways over the course of about 30 hours and I didn’t find any shorts… but my guess is that I nudged something out of the way while doing my clean up so it now works… I’m dumbfounded.

Now to dig in and see if I can find out what the problem was in the first place.

And also… THANK YOU for your help! You and the others who have posted here lead me to poking around in the amp and, whatever happened, it made it work!

 

[D'tar]

Sweet! Grab a new full voltage chart while things are functioning please!

 

[Camdenharr]

Sweet! Grab a new full voltage chart while things are functioning please!

Good call I’ll work on this today!

 

[D'tar]

If you don't mind posting it and label it as

Bassman Micro LTP Voltage Chart

those who are looking for reference voltages can easily find them. I could not come up with a good source without too much effort.

thanks

 

[Camdenharr]

The following are my DC voltage readouts for a fully functioning Micro Bassman LTP, as designed by @robrob

Thanks again to the fantastic community here for helping me get this thing into rock n' roll shape - it sounds GREAT.

B+1: 314.6
B+2: 312.7
B+3: 258.9

Pins in vDC	V1 (12AY7)	V2 (12AX7)	V3 (12AX7)	V4 (12AU7)	V5 (EZ81)
1	135.5	145.5	198.2	312.8	118.9
2	0	0	17.2	0	0
3	2.2	.965	27.05	9.4	313.4
4	9.75	10.1	10.1	9.52	9.87
5	9.75	10.1	10.1	9.52	9.91
6	135.1	259.2	197.4	313.7	0
7	0	145.2	17.9	0	119.3
8	2.2	145.3	27.02	9.8	0
9	9.88	10.07	10.02	9.8	0

 

[Camdenharr]

Sweet! Grab a new full voltage chart while things are functioning please!

Hello sir - I just posted the functioning voltages for the amp. They're pretty similar to what I had before but definitely some differences. This thing sounds great - thanks again for the help!

I couldn't see how to edit the initial post (not sure if I even can) to reference that the correct voltages for the properly operating amp are in post #26.

 

[robrob]

@Camdenh, thanks for posting the voltage chart. What power transformer did you use?

 

[Camdenharr]

@Camdenh, thanks for posting the voltage chart. What power transformer did you use?

I used the Hammond 270ax PT for this one

 

[dbyington]

You're probably not going to like this one, but I did the exact same build (with a slight mod to the input section) a year ago and had very similar motorboating/oscillating type issues. But I'm lame and didn't post the build, started to but got so excited I ended up doing an embarrassing job. And then redid most of it, twice.

any luck chop sticking the circuit? do any of the pots influence the motorboating/noise?

Do not overlook this!
I tore my build down twice and found at least 3 bad solder joints. Once those were fixed all issues were gone. It's a wonderfully sounding amp now.

 

[Camdenharr]

You're probably not going to like this one, but I did the exact same build (with a slight mod to the input section) a year ago and had very similar motorboating/oscillating type issues. But I'm lame and didn't post the build, started to but got so excited I ended up doing an embarrassing job. And then redid most of it, twice.



Do not overlook this!
I tore my build down twice and found at least 3 bad solder joints. Once those were fixed all issues were gone. It's a wonderfully sounding amp now.

Amen my friend. I got it all working awhile ago. It sounds killer.