New clone build - observations & feedback accepted

[badfan]

Hi everyone,

I have recently built a dumble clone based on the ceriatone kit parts including building all boards myself etc however I have the following differences.

1. Used spare bassman type PT, OT and choke (5H/100ohm) that I had from a previous build not completed
2. Used my own steel chassis etc.
3. Separate relay transformer
4. 50watt 2xEL34 based output

Apart from a slight 'squeeze' to fit all boards / components everything has come out really well all test OK etc and everything appears normal.

I have a slight problem in that footswitch LED's are reversed ie when OD is on the LED is off (is this right) however this wont take long to sort
NB I reversed the layout due to my chassis and this being a head type format so probably cocked something up in the conversion.

Anyway the PT I am using has 2 secondary options being 360-0-360 or 330-0-330. When I initially planned the build I intended to use 330-0-330 which gets me quite near the B+ voltages mentioned however when I first built the amp I connected the 360-0-360.

After initial testing / burn in etc and after playing for a bit the response / sound of this amp is absolutely excellent. Full sounding, rich harmonics, a sort of of dynamic feel that I have not experienced in an amp before and everything seems alive.

Anyway when I measured the voltages they looked high (based on previous posts / #124 schematic etc) so I decided to switch to the 330-0-330 secondary to reduce the voltages etc. After playing for a bit something for me is lacking is does not seem as 'rich' sounding as previously. I have fiddled with the OD trimmer etc and although a get a very passable sound it just seems to lack something?.

I am waiting for my 'new' digital oscilloscope so that I can start to look at what is going on in more detail but for now here are the voltages for both secondary options

Can anyone confirm if the voltages look reasonable and why I may be getting a bettrer sound with more 'juice' (all subjective of course) NB my 240 wall voltage is also slightly on the high side.,..

Secondary 360x360 330x330
B+1 487 449
B+2 477 448
B+3 460 433
B+4 375 352
B+5 371 349

V1 225 1 209 1
2.24 3 2.09 3
230 6 213 6
2.1 8 1.99 8

V2 229 1 213 1
2.19 3 2.04 3
202 6 187 6
1.46 8 1.35 8

V3 272 1 252 1
56 2 52 2
83 3 78 3
277 6 258 6
66 7 59 7
83 8 78 8

V4 476 3 446 3
468 4 441 4
-35 5 -35 5
479 6 447 6

V5 475 3 446 3
467 4 441 4
-35 5 -35 5
478 6 448 6


Cheers
Sean
________
RHODE ISLAND MARIJUANA DISPENSARY

[dogears]

Sean, looks like something is wrong with your PI tube. You should be well over 300V with the 360 tap and I'd expect around 290-300V on the plates with the 330 tap.

[badfan]

Sean, looks like something is wrong with your PI tube. You should be well over 300V with the 360 tap and I'd expect around 290-300V on the plates with the 330 tap.

Dogears a big thank you & spot on... just changed the tube for a spare one I had and the voltage is now showing 290 with cathodes around 57. V1 voltages are in the 203 ball park now and after a quick play some 'sparkle' has returned

Thanks for your help. Should have noticed that myself

On a seperate note what do you think about the different taps? is there a better one to use with EL34's etc. I only ask as the OT is is not suitable for 6L6 due to impedence etc abd up until now I have been more a Marshall focused builder especially a warmed up 2203/4 circuit which seems to benefit from higher B+ for the power tubes.

Cheers
Sean
________
DEMEROL REHAB DICUSSION

[dogears]

Sean,

Try the 360 tap. Make sure you either have a FET or the simulator resistor to ground off of the V1 node (150K)

Then, try a 6.8K to 8.2K resistor to drop the voltage to the PI, which will aslo get you where you want to be on V1 and V2.

Lastly, the non-inverting side of the PI should have about 6 more volts than the feedback side. In other words, 1st half should have a smaller plate load and a little more voltage. Try setting between 12 and 18 K difference between plates using trimmer. Play low E notes with OD on. Turn trimmer for best feel and "thud". Loud.

BTW, try a new V2 tube as well. Cathode voltages are wacky...

Glad to help.

[ic-racer]

I have a slight problem in that footswitch LED's are reversed ie when OD is on the LED is off (is this right) however this wont take long to sort
NB I reversed the layout due to my chassis and this being a head type format so probably cocked something up in the conversion.

I used the Ceriatone relay boards also and the OD board is wired for CLEAN when the relay is energized.

I had a post about this somewhere, but I rewired the relay (under the board) so that it works the other way around. Then I re-wired the DPDT switch on the footpedal. Once it is wired like (OD ON = RELAY ENERGIZED = LED ON) this you theoretically can use just a SPST switch on the footpedal.

[heisthl]

Your footswitch can work either way, here's a handy guide to both kinds :

[badfan]

Guys thanks for the suggestions and the help with the LED's. I will get round to these over the next day or so.

I should have mentioned I have not installed the FET board in this build, but I also dont recall that I have added an additional 150k simulation resistor? excuse my ignorance but why is this needed, and where on V1 should it go.

Regards
Sean
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GIFT CARDS

[heisthl]

Fet simulator resistor can go anywhere, one end on any point that has B+5 and the other end to the ground point that B+5 uses. It is necessary to provide a "draw down" at the end of the string to make the dropping string work the way HAD intended and also has the added benefit of providing a bleed off path for the caps when the amp is off (remember to put the standby in operate position to bleed off B+1).