12ax7-ecc99 tube amp

[WhenBoredomPeaks]

Since the topic pretty much is about OTs now, i would inlude a small question.

I have a higly modded Champion 600 with switchable cathode bypass for lower bass response, new tubes, appropiate cathode resistor on the output tube, bypassed tonestack, upgraded coupling caps, variable NFB and i bought a new speaker (Jensen C8R) which i play sometimes without a cab, just for breaking it in.

The thing sounds really nice clean, but when i turn the volume up, the highs are getting harsh and fizzy. I one played the amp with in-ear phones which lock the treble better than the bass and i liked the tone much better.

Cna the shitty stock output transformer cause the bad treble response?

[GibsonGM]

Or the speaker?  Sometimes it's the cab, and if the spkr is on the floor, it'll do weird things...

[WhenBoredomPeaks]

Or the speaker?  Sometimes it's the cab, and if the spkr is on the floor, it'll do weird things...

The stock speaker is dark actually and bad sounding but both of the speakers doing it when i crank the amp. The stock speakers fart badly too, the small cab and the weak speaker can't take it. The Jensen doesn't fart, it is just harsh. And when i will put the Jensen into a cabinet (which i should have done 2 weeks ago but the local carpenters don't glue wood and they use only sh*tty particle boards and i don't have any wood working tools) that won't solve the high end harsness imo. (i know that the lower frequencies can block each other out so it sounds thinner of course but the high end should be much milder)

It sounds nice when i "overdrive" the clean amp with a pedal. But when i just crank up the amp it starts to sound harsh, so thats why i think that the crappy stock OT can't take the increased volume.

Since i bypassed the tonestack with a 0.022uF Orange the EQ should be flat.  Plus the midrange and bass is definitely there because it sounded quite good when i had an inear phone in my ears which blocks high frequencies easier than bass or mids so it is a bit like an equalizer with the treble turned down.

[GibsonGM]

Wow, those are some odd symptoms, man. What are the output tubes? EL-84's can sound really fizzy if they're pushed hard. My 18W currently does that when I crank it too much (need to increase power tube grid stoppers & decrease PI tail resistors). Maybe you've got something like that going on?

[WhenBoredomPeaks]

Wow, those are some odd symptoms, man. What are the output tubes? EL-84's can sound really fizzy if they're pushed hard. My 18W currently does that when I crank it too much (need to increase power tube grid stoppers & decrease PI tail resistors). Maybe you've got something like that going on?

The amp is a modded Champion 600 reissue.

Stock OT and PT.

Tung-Sol 12AX7 preamptube and a JJ 6V6 output tube.

Tonestack bypassed with an Orangedrop 0,022uF cap so it is like a 5E1 circuit now. Cap between the preamptube and the powertube is changed to a Orangedrop.

Feedback resistor is switchable between stock and no feedback but it is not the source of the problem, its fizzy at both settings.

There is a switchable cathode bypass cap (stock 22uF and 2,2uF) at the first half of the preamptube for less bass.

I saw a post somewhere that the amp is like factory misbiased. Fender raised the B+ without changing the bias of the tubes or something like that.

- One thing that this amplifier invariably needs is power tube bias adjustment. The Champion 600 Reissues that we have seen have had the 6V6 power tube biased for too much power dissipation. The correct power dissipation for a 6V6 is considered to be between 12W and 14W (12W for vintage 6V6s and up to 14W for some of the newer 6V6s). The Champion 600s that we have seen were biased for between 15.5W and 16.5W. This is simply too high and does not sound optimal. We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.
Your measurements are absolutely correct... it's Fender's design which isn't .

So i changed the 6v6 cathode resistor to a 680ohm one.

My voltages:

All my measurements are DC:

TP2: 218VDC (First input triode plate voltage)
TP6: 1,63VDC (First input triode cathode voltage)
TP5: 218VDC (Second input triode plate voltage)
TP7: 1,7VDC (Second input triode cathode voltage)

TP9: 347VDC (Output tube plate voltage)
TP8: 21,4VDC (Output tube cathode voltage)

TP10: 336VDC (B+ after two resistors)
TP11: 355VDC (B+ after one resistor)

A schem of the stock amp: http://www.schematicheaven.com/fenderamps/champion600_reissue_fullmanual.pdf


As xou can see i did a lot to get rid of the problem, i did the steps one by one, during a 1 month period on the weekends, the amp got better step-by-step, i even get rid of the low end rattling when the amp is cranked (after i changed the cathode bypass resistor of the 6V6) with the Jensen, but the too dominant high end harsness is still there.

Thats way i think the only stock stuff left is the transformers which could be bad, or something is wrong in my circuit, like something gone wrong or i don't know.

[armstrom]

I have contacted the vendor in Germany who sells the small toroids. He says if we can get together an order of 5-10 transformers he could have them built with 120V primaries and keep the price the same. (22 euros). I'm not sure at this point what shipping would run. Keep in mind that the 22 Euro price includes German VAT (a sales-tax built into the price). I would have to check but there's a good chance that we wouldn't have to pay that 19% since the part is being exported outside the EU, however I'm not 100% sure as I've just begun discussions.

So, the real question is, how many people are interested? And for how many transformers? I would probably pick up more than one myself just to have an extra on hand should I want to build another low power tube project. I would be willing to organize this and handle the single order and shipment from Germany then do the redistribution here in the US.  I have no idea about shipping or lead-times right now but I wouldn't expect this to be a very quick process since the trannies would have to be manufactured then shipped from Europe.

I'm also looking into manufacturers here in the US but so far no one has been able to get close to the small size / low price of the German transformers. If the super small size isn't an issue I may have a good solution for a similar price, but I'm waiting to hear back on that.
-Matt

[Brymus]

Wow, those are some odd symptoms, man. What are the output tubes? EL-84's can sound really fizzy if they're pushed hard. My 18W currently does that when I crank it too much (need to increase power tube grid stoppers & decrease PI tail resistors). Maybe you've got something like that going on?

The amp is a modded Champion 600 reissue.

Stock OT and PT.

Tung-Sol 12AX7 preamptube and a JJ 6V6 output tube.

Tonestack bypassed with an Orangedrop 0,022uF cap so it is like a 5E1 circuit now. Cap between the preamptube and the powertube is changed to a Orangedrop.

Feedback resistor is switchable between stock and no feedback but it is not the source of the problem, its fizzy at both settings.

There is a switchable cathode bypass cap (stock 22uF and 2,2uF) at the first half of the preamptube for less bass.

I saw a post somewhere that the amp is like factory misbiased. Fender raised the B+ without changing the bias of the tubes or something like that.

- One thing that this amplifier invariably needs is power tube bias adjustment. The Champion 600 Reissues that we have seen have had the 6V6 power tube biased for too much power dissipation. The correct power dissipation for a 6V6 is considered to be between 12W and 14W (12W for vintage 6V6s and up to 14W for some of the newer 6V6s). The Champion 600s that we have seen were biased for between 15.5W and 16.5W. This is simply too high and does not sound optimal. We have found that the installation of a 200 Ohm to 240 Ohm 2W resistor in series with the factory installed 470 Ohm resister in R10 will achieve approximately 12W to 13W power dissipation.
Your measurements are absolutely correct... it's Fender's design which isn't .

So i changed the 6v6 cathode resistor to a 680ohm one.

My voltages:

All my measurements are DC:

TP2: 218VDC (First input triode plate voltage)
TP6: 1,63VDC (First input triode cathode voltage)
TP5: 218VDC (Second input triode plate voltage)
TP7: 1,7VDC (Second input triode cathode voltage)

TP9: 347VDC (Output tube plate voltage)
TP8: 21,4VDC (Output tube cathode voltage)

TP10: 336VDC (B+ after two resistors)
TP11: 355VDC (B+ after one resistor)

A schem of the stock amp: http://www.schematicheaven.com/fenderamps/champion600_reissue_fullmanual.pdf


As xou can see i did a lot to get rid of the problem, i did the steps one by one, during a 1 month period on the weekends, the amp got better step-by-step, i even get rid of the low end rattling when the amp is cranked (after i changed the cathode bypass resistor of the 6V6) with the Jensen, but the too dominant high end harsness is still there.

Thats way i think the only stock stuff left is the transformers which could be bad, or something is wrong in my circuit, like something gone wrong or i don't know.

Off the stock schematic I would try raising R17 to 10K or higher that should tame the "high end" some.

[Brymus]

I have contacted the vendor in Germany who sells the small toroids. He says if we can get together an order of 5-10 transformers he could have them built with 120V primaries and keep the price the same. (22 euros). I'm not sure at this point what shipping would run. Keep in mind that the 22 Euro price includes German VAT (a sales-tax built into the price). I would have to check but there's a good chance that we wouldn't have to pay that 19% since the part is being exported outside the EU, however I'm not 100% sure as I've just begun discussions.

So, the real question is, how many people are interested? And for how many transformers? I would probably pick up more than one myself just to have an extra on hand should I want to build another low power tube project. I would be willing to organize this and handle the single order and shipment from Germany then do the redistribution here in the US.  I have no idea about shipping or lead-times right now but I wouldn't expect this to be a very quick process since the trannies would have to be manufactured then shipped from Europe.

I'm also looking into manufacturers here in the US but so far no one has been able to get close to the small size / low price of the German transformers. If the super small size isn't an issue I may have a good solution for a similar price, but I'm waiting to hear back on that.
-Matt

I am interested but I wont have any funds to commit to that for at least two months or more.
I bet some others here would want one as well.

[punkin]

Do you hae more details?...number of secondary outputs, voltages, current handling etc.?

[armstrom]

Sure. As of right now I would just be asking for a change to the primary winding so the secondaries would stay the same as the standard transformer which are:

185V @ 40 mA HT
6.3V @ 1.4A Filament

Neither secondary has a center-tap so a bridge rectifier is needed on the HT and 100ohm resistors will need to be used on the 6.3V heater secondary to create a "virtual" center tap. Nothing unusual. This is the exact transformer used int he initial schematic first posted in this thread so you can use it to build the amp as shown with no changes. Since this amp is nearly identical to Dough Hammond's firefly you could use the transformer for that amp as well. Finally, you could use it for all sorts of high voltage tube preamps / stompboxes. You wouldn't be able to use a super small enclosure but at 63mm (~2.5") in diameter and 31mm (~1.2") tall it should fit in lots of tight places.

-Matt

[armstrom]

Hmm.. so not as much interest as I would have hoped oh well. I'll keep trying to dig up cheap alternative power transformers.

[rutabaga bob]

referring back to rotylee's comment, thinking about 6sn7 as an alternate for the ecc99...i have been thinking similarly,
along the lines of a 6cg7, which is the 9-pin equivalent of the 6sn7.

[rotylee]

datasheet
http://www.drtube.com/datasheets/6cg7-ge1956.pdf

[rotylee]

found updated schematic
http://diyguitarfreak.files.wordpress.com/2010/09/miniamp2-schematic.jpg
from blog post
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168

[FcKw]

found updated schematic
http://diyguitarfreak.files.wordpress.com/2010/09/miniamp2-schematic.jpg
from blog post
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168

It's actually not an update but a new mini guitar amplifier I built with two 12AX7s in the preamp and an ECC99 in the poweramp, providing a full tone stack and a "real" push-pull design with a phase-inverter. Only thing similar are two of the three tubes.  

here are some soundsamples:
http://www.youtube.com/watch?v=lOb-RVET8So

greets
Patrick

[Brymus]

found updated schematic
http://diyguitarfreak.files.wordpress.com/2010/09/miniamp2-schematic.jpg
from blog post
http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168

It's actually not an update but a new mini guitar amplifier I built with two 12AX7s in the preamp and an ECC99 in the poweramp, providing a full tone stack and a "real" push-pull design with a phase-inverter. Only thing similar are two of the three tubes.  

here are some soundsamples:
http://www.youtube.com/watch?v=lOb-RVET8So

greets
Patrick

Thats sounds absolutely fantastic !!
I listened to your demo and found the link to your blog. http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168
I was going to ask for a schematic but you alreadt posted it there .
THANK YOU !

IMO this amp is worthy of its own thread.
And nice job again, on the demo and the blog.
+1

[FcKw]

Thats sounds absolutely fantastic !!
I listened to your demo and found the link to your blog. http://diyguitarfreak.wordpress.com/2010/09/15/the-miniamp-2-0/#more-168
I was going to ask for a schematic but you alreadt posted it there .
THANK YOU !

IMO this amp is worthy of its own thread.
And nice job again, on the demo and the blog.
+1

Thanks! OK, I started a new thread including the schematic HERE.