TC 8W Tube Amp Project

TomCat · 2009-07-10T18:13:17+00:00

Ok.....I decided to start a new thread following from Karel's thread about his 5W amp project. I've decided to go for a 8W Class A Amp head as a project. I...

TC 8W Tube Amp Project

Sean

Nice one Tom! Even though you are still waiting for the Celestion speaker, how about some sound clips. We want to hear it! It will also be helpful (at least to me) if you record again later with the Celestion. I would like to hear the difference. Well done on completing a great project ?

TomCat

Sean wrote: Nice one Tom! Even though you are still waiting for the Celestion speaker, how about some sound clips. We want to hear it! It will also be helpful (at least to me) if you record again later with the Celestion. I would like to hear the difference. Well done on completing a great project ?

Clips coming soon......I'll probably record something at church to get a decent recording.....will take a day or 2 to do.....

FenderBender

Awesome Tom!

I'd love to see a few pics of the finished masterpiece ?

TomCat

Pics time.

The amp is not finished yet but here are a few pics to show where things are currently at.

Chassis with Tranny's and Tubes

Tubes fired up and ready to go

Starting the Cab Build

Vent In the Top Panel of the Cab

Completed Cab waiting for internal painting and Tolex

More Pics to come soon.

racman

Looking fantastic Tom !! ? ?

TomCat

Another picture of the amp inside the cabinet with the front panel in place.

TomCat

Another update time and a few more pics.

Got my Caps for the cascade preamps (V2 a&b) from Matta today.

Wired all in and fired up again......

Clean channel first...All is well

Switched over to OD and nearly blew the windows out.......OMG was there gain and level.....could not turn the OD level over about 1 out of 10. Anywhere above about 4 and the amplifier went into feedback.....internally and the tone was not great.....very flabby.

Added a voltage divider in between the two stages and dropped the input impedance to the second stage. Tone now a lot better but uncontrollably loud. The drive range was OK but the output level was way too hot. I have added a voltage divider to the output of the second stage ans this brought the levels under control. There is still a lot of level but the OD level can be turned up to about 8 before the amplifier begins to oscillate with the drive control at full drive. there is a slight hum on the OD level control I need to track down and get rid of.

I'm loving the OD sound on this amp. Depending on the settings you can go from light overdrive on the bridge to really dark crunch using the neck PUP with the EQ bypassed. And all this using the loudspeaker from Mariann's little Vox Pathfinder 15 cabinet loaded with a cheapie 8" loudspeaker.

I cant wait to hear this thing through a 12".

A also replaced my 6CA7 with one of the Electro Harmonix tubes I had in my stock...What a difference...lots more level and sparkle out of the amp. I think the other tube is old and a little tired. The OD also sounds more three dimensional and seems to have more depth.

Some more Pics:

Bottom of chassis showing the components/wiring

My Test Setup. Amp driving stripped Pathfinder 15

Front View with power on. Thanks Matta for the Knobs...Looks really cool. You are Karma'd/Thanked

Still working on some clips....please be patient......

matta

Tom ?

It looks awesome, kudos!

TomCat wrote: Front View with power on. Thanks Matta for the Knobs...Looks really cool. You are Karma'd/Thanked

My pleasure, no thanks was needed, glad I could contribute something small to your project.

Matt

WantzChas

Very interesting read, keep up the good work Tom. Can't wait for sound clips...

MikeM

Today Gearhead and I were having an in depth discussion of the implications involved when using 2 extra gain stages from an additional 12ax7.. Seems the voltage divider works but perhaps do some research about adding a tone stock for some insertion loss? Can't remember if you have a proper one or not.

TomCat

@ Mike

My current configuration is:

Preamp 1 -> Tone Stack -> Drive -> Preamp 2 -> Preamp 3 -> Volume -> Preamp 4 -> 6CA7 O/P.

Preamp 2 & 3 are the two cascaded stages and are switched in to provide the OD. I had too much level after Preamp 3 and therefore added a voltage divider between Preamp 3 and the volume control.

The second issue I had was the general tone of the OD and I simply reduced the input impedance into preamp 3 which seemed to tidy things up.

Gearhead

I just like the sound of the MesaBoogie Studio and studying the schematics:

... made me realise Randall Smith uses a lot of capped voltage dividers between the many gain stages to keep the tone intact. Just have a look on TubeFreak.com

matta

You guys and your cascaded gain stages... I think Tom is a wannabe Metal Rocker in diguise ?

Matt

Karel-Mars

Nicely done Tom! Your wiring is very neat.

TomCat

Thanks Karel.

I must say that this has been a fun project and I have learned huge making this amplifier.Looking forward to completing it now and moving onto something new.

I did a bit more work on it last evening and found I had made a mistake wiring the tone stack. I've corrected it now and the amp now sounds even better. I also spent a bit more time on the cascaded pre stage and it's now sounding better as well.

As promised....clips will come soon.

TomCat

A quick question...

The 6CA7 is emitting a small blue glow on one side near the base of the tube....Have I biased the tube a little hot or is this normal. When I switch the amp into standby it dissapears.

Amp is sounding great and appears to be working normally......

Any comments.....

Edit.....Just Google'd the blue glow and it appears that what my tube is doing is normal........small blue glow near the glass envelope....Phosphorescence of electrons on the glass envelope.....looks cool though.....

matta

Hah Hah,

Was just about to tell you that, perfectly normal, and beautiful to watch!

Red plating on the other hand is not so fun...

Matt

TomCat

matta wrote:
Hah Hah,

Was just about to tell you that, perfectly normal, and beautiful to watch!

Red plating on the other hand is not so fun...

Matt

Haha....fortunately, I don't have that.

TomCat

Some more Pics

Front View Head and Cab

Front View Head

Rear View Head and Cab

Head, Cab and Guitar

Next week I'll be doing the covering of the cabinets.

Hopefully soon I'll get the loudspeaker.

kayDUB

Awesome! now get that tolex on! ?