7-Octal: Rockster plus?

[Phil_S]

Hi Zippy. Already there with the 25K pot! It is in the front panel waiting for it's turn. What do they say? Brilliant minds....

How about the dual MV pot? How do I know both will be in sync?

[matt h]

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[Phil_S]

Hi Matt. This is an area where I am easily flumoxed from overthinking it. Meanwhile, I was about to say, "nevermind" because I found it on the internet. Back to the salt mine...

[Phil_S]

Nearly done. Needs to be verified against the schematic. Needs quite a bit of solder, too! I prefer to wait to solder most stuff after I verify it. I am guessing it will make noise next week sometime.

[matt h]

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[Structo]

Looks good Phil but my God man!
Straighten up those electrolytics before the OCD folks chime in.

[Phil_S]

Once there is solder on the joints I'll be able to dress it a lot neater. Things are wiggly right now and it's a good thing because I needed to slip things underneath. It was really challenging to figure out what should be done first! In some cases I could simply push things out of the way!

[matt h]

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[Phil_S]

Read here: https://tubeamparchive.com/viewtopic.php?p=276805
Basically, a big ass resistor that came with the amp and, well, who could resist? As for what you make of it in your mind...I'm not responsible for that!

[Phil_S]

I think I'm going to call it the Roctal7. First power up this morning went without problems and I'm getting a minor pop at the test speaker from V1, so I'm reasonably sure the signal chain is OK. I have first voltage readings.

I think there is some problem with the 6SJ7. It only has cathode voltage on position #3, input at the top .047 coupling cap to the PI. On the other 3 settings there is no cathode voltage. Any thoughts?

I'm thinking the volt drop between C and D in the B+ supply across the 47K is more than what is desirable, giving 190-ish B+ nodes for the three preamps. Any thoughts on what you think is a better voltage? I know I want to get the 6SJ7 to at least 140V on the plate.

Pictures will follow shortly.

Page back to my 12/20/13 post for a schematic, but V#'s aren't right. The chart makes clear which tube is which.

Not on the chart, B+ nodes:
A 449
B 448
C 349
D 190.8
E 190.4
F 190.2

I don't think this is ready for prime time just yet and have not brought it up from the basement to plug in a guitar. (Guitar not possible in my basement -- just a small room under my dining room and crowded with all manner of stuff including work bench, furnace and water heater.)

I have a scope, several meters, and rigged an old laptop to be a sig gen, but never tried it out as such, should we need to get into some diagnostics.

[Phil_S]

Pictures...the rotary switch for the 6SJ7 is mostly at the top left corner. Three tubes from top to bottom:
6SJ7
6SL7 V1 input from jacks
6SL7 V3 LTP PI

Tube to the right of the 6SJ7 is V2, gain stage and cathode follower.

From left to right, front panel knobs:
6SJ7 volume
Volume
Bass
Mid
Treble
PPIMV is on the rear, probably not seen in these pictures. Pictures may require multiple posts.

[Phil_S]

more...

[Phil_S]

Oh, we got trouble...

Two problems at least. I've pulled the switch for the 6SJ7 and the tube. More on that later. Let's see if someone can help me on the basic DC30 without the pentode. Let's deal with the pentode later.

I have modified the B+ ladder, swapping a 10K for the 47K with some success. I might use a 5K, but that isn't creating my problem. Voltage readings changed some, but all are reasonable.

With some effort, I realized the schematic I drew has an error and I built the schematic. On V1, I moved the 560p from the grid on V1 to the plate, then linked the two grids for parallel input. You will see this error on the coffee&cream colored 560p in the pictures. That completed the signal chain and I've got pops in all the right places when I probe. However, guitar volume is nearly non-existent...like maybe 1/10W sound-wise and very fizzy.

So, the good news is that the signal chain is operating and all voltages are reasonable. The bad news is the amp doesn't really work.

One minor problem I noted is the error on the input jacks of using a 1.5M where I should have used a 1.0M. I don't imagine that is the problem though.

Honestly, I don't know what I'm looking for. This sort of problem is new to me. My amps tend to work right out of the box.

I am thinking this is something simple, but I am at a loss on how to find it. Remember, I'm an amateur. My trouble shooting skills are incomplete.

Thanks for any suggestions you might have.

[surfsup]

It doesn't look like you tied your grids together on V1.

[Phil_S]

Surf...please read what I wrote above your post, paragraph that starts, "With some effort..."? I didn't post new pictures.