Ceriatone Stray Cat 30 Issues

[bal704]

I'm in the middle of a scratch build of a Ceriatone Hot cat 30 clone. I also talked about this in another thread:

https://tubeamparchive.com/viewtopic.ph ... 474#237474

Schematic here:
http://www.webphix.com/schematic%20heav ... cat_30.pdf

Layout here:
http://ceriatone.com/images/layoutPic/m ... iatone.jpg

The only differences from the Ceriatone layout are the addition of a 3rd channel (EF86) and the VVM circuit discussed previously.

The amp is up and running, with my B+ running around 350V versus about 380 on the schematic. Voltage at pin 3 on the power tubes is 343 V versus 376 V on the Schematic. The voltages I'm measuring are about 20-30 volts lower than the stated schematic voltages, but otherwise consistent with the schematic voltages.

A couple of issues:

1) I've got a buzz in the gain channel. Using an audio probe, there is very little hum before pin 2 on V2b (measured before the 470k resistor). However, there is a lot of buzz measured at the Edge pot. Given that there are only a couple of parts between the 2 places, is it normal to have that much buzz introduced? I replaced the tube and it didn't help.

2) When plugged into only the clean channel, gain channel master at zero, I get no buzz. Turning up the gain channel master introduces buzz into the sound. When I turn the clean channel volume to zero, and turn up the gain channel master, I get guitar sound out of my speakers.

If I'm reading the schematic correctly, I should be getting no sound out of the speaker, since the only channel with input (clean) is at zero volume. Basically G on the schematic is at zero, and there's no input to feed F, so it should be at zero. How is it possible to be getting sound?

[gingertube]

You have a wiring problem somewhere which is causing 2) above and may be contributing to 1) as well.

Try to check your wiring against the SCHEMATIC and NOT the layout.

There is an issue with schematic / layout consistency.

For some forgotten reason the CONVENTION when using twin triodes like the 12AX7 is that the pin 6,7,8 unit is called the A part (as in V2A) and the pin 1,2,3 unit is called the B part as (in V2B).
Why did I use V2 as my example - well looking at the layout then V2 on the schematic follows thos convention whereas V1 on the schematic is labelled opposite this, V2 is "correct". I did'nt check further.

Take your schematic and go through it and number the pins, then check your build against that.

Cheers,
Ian

[bal704]

Thanks for the reply. I'll double check everything. It appears if you don't follow the convention, and you have multiple tubes, it would easy to get the layout double-crossed with the schematic.

[bal704]

I’ve been comparing the schematic and layout, and here are the major differences I see

1) Resistors on Gain input are swapped on the layout vs Schematic. They’re both pretty big, so not sure it matters but I’ll swap them.
2) The schematic has the middle lug of Edge pot to ground, with a 10n cap to lug 3. Layout has lug 1 to ground, and the 10n cap to middle lug. Basically the layout is shifted over 1 lug from the schematic.
3) The schematic has a 220k resistor between the middle lug of the Treble and master pots. The layout has the resistor to lug 3 of the master.
4) The inputs to the PI on the layout are reversed from the schematic between gain and clean.

I’ll make these changes and see what happens. Ceriatone has pictures up on their website of a completed build. It appears they followed the layout, not the schematic.

[bal704]

OK. I made the changes detailed above.

1) Still have the buzz
2) With the changes, the cross talk between channels is now controlled by the gain knob. In other words, plugged into the clean channel with clean volume zero, I can get guitar sounds by turning up the gain knob, but not the master.

The amp does sound really good. The gain channel is nice and lush. I like the sound of the amp better when it matches the layout (and the Ceriatone pictures). The sound is fuller, if that makes sense.

Also, I find I like the sound best when the VVM is cranked to full voltage, so I may pull out the VVM circuitry and just install an ON/OFF switch.

[bal704]

I got rid of the VVM, and replaced it with an On/Off switch. Also, I usually hook the heater CT to ground, but I had read about 'elevated heaters' and this time I hooked them to the Pin 1 Cathodes. I swapped the CT back to ground, and it really helped with the buzz I noted above.

When I fire the amp up, missing only the power tubes, and use the audio probe, it sounds pretty good. The buzz sounds like it's decreased. However, once I plug the power tubes in (EL34), I get a very loud hum. I swapped the OT leads to see if that would help, and it turned into a loud hum with squeal.

This is my only EL34 amp. I have several 6L6 amps. I have hooked pin 1 and Pin 8 together on my tube sockets. Is it possible to install the 6L6 tubes into the amp to see if the problem lies in the power tubes? I realize the bias will be off, but will it be possible to run it for 30 seconds or so to see if the other problems are fixed? I'd like to find out if the problem really lies in the tubes before I buy another pair.

[M Fowler]

Power tube imbalance can be a problem but also the bias cap is another area that can cause a hum. But this is cathode bias if memory is correct.

[Diablo1]

When I fire the amp up, missing only the power tubes, and use the audio probe, it sounds pretty good. The buzz sounds like it's decreased. However, once I plug the power tubes in (EL34), I get a very loud hum. I swapped the OT leads to see if that would help, and it turned into a loud hum with squeal.

This is my only EL34 amp. I have several 6L6 amps. I have hooked pin 1 and Pin 8 together on my tube sockets. Is it possible to install the 6L6 tubes into the amp to see if the problem lies in the power tubes? I realize the bias will be off, but will it be possible to run it for 30 seconds or so to see if the other problems are fixed? I'd like to find out if the problem really lies in the tubes before I buy another pair.

When you swapped the OT leads, you were getting positive feedback that caused the squeal. You need to put the leads back the way they were. You can swap in 6L6 tubes with the way you have the sockets wired. #1 pin on a 6L6 is not connected internally to anything. What are you using for a PT, OT and choke? You mentioned your voltages are off, and it could be your PT. If you are using the TDS transformers, my guess is that your voltages would exactly match the schematic. I used the TDS transformers in my Ceriatone DC30 build and followed their layout and grounding scheme. Their layout matched the DC30 schematic with no mistakes, and my amp is dead quiet. I would double check all your wiring vs the Ceriatone layout. My voltages also exactly match the DC30 schematic.

[bal704]

I'm using a 330-0-330 PT from Musical Power Supplies. The layout calls for a 325-0-325 PT. I tried multiple times to get in touch with TDS, but no luck. So I went with plan B.

I'm using a MM choke, and a VOX AC30 ClassicTone OT, which was recommended by Nik.

The voltages on the schematic are for a tube rectifier, and I'm using a SS rectifier.

I plugged in some 6L6 tubes, and the amp fired right up. However, I still get the buzz. I noticed that when I turn the Master Vol to zero, I can hear the buzz from the PT that I described in the previous thread (linked above). Then when I increase the MV, the buzz get louder.

Other than the buzz, the amp sounds really good. Nice lush distortion. Happy with the sound, other than the buzz. I'll keep looking for some layout issues, and I've contacted the PT vendor to see if he has any tips for me.

Thanks for the help.

[Reeltarded]

Exact same buzz gets louder? Listen to it very closely.

Idle buzz with everything on zero points to something after the last point of control. Identical buzz as volume increases indicates a probable ground loop... at least likely.

[bal704]

When all volumes are at zero, I get no buzz. The amp chassis is about 2 feet from the cabinet. At zero volume, I can put my ear up to the chassis and hear a certain frequency buzz coming from the PT. When I turn up the volume, that same exact frequency buzz is what's coming throught the speakers.

Turning up the volume makes the buzz and guitar louder.

[Diablo1]

When all volumes are at zero, I get no buzz. The amp chassis is about 2 feet from the cabinet. At zero volume, I can put my ear up to the chassis and hear a certain frequency buzz coming from the PT. When I turn up the volume, that same exact frequency buzz is what's coming throught the speakers.

Turning up the volume makes the buzz and guitar louder.

If you can hear a buzz from the PT at no volume, that tells me that your PT laminations are vibrating due to AC line voltage switching the magnetic field back and forth. I think the PT was not built/assembled correctly. See if the manufacturer agrees, and will send you a new one. If not, you may just have to switch to a different manufacturer.

[bal704]

I'm in contact with the PT Mfg. I noticed when I got it in the mail it had a distinct smell of lacquer or somthing similar. Never had one smell like that before. The smell went away after a few days, but it was strong enough for others in my house to notice.

[M Fowler]

Here is an interesting Hot Cat build

http://pauledwards.co.uk/gallery/index.php/30w

[zelenko]

Hello, im having the same issue, buzz when master is engaged, the clean channel works good! i doubled checked everything and there is no mistake to the wiring!
did u solve your problem?
thanks in advance