Dr. Z RT66

vanessa · Post by **vanessa** » 27 Jul 2007, 03:57

Enjoy!

soulsonic · Post by **soulsonic** » 27 Jul 2007, 06:13

Hmmm... that looks like it wouldn't be a very difficult DIY build. Thanks for the scheme!

bajaman · Post by **bajaman** » 27 Jul 2007, 09:12

Thanks V
I built one of these a few years ago - still not sure whether I like it or not - very odd tone controls and what is the purpose of that 10 k resistor in series with the phase Inverter stage 12AX7. I have a friend who had one of these and yes your schematic is correct, he didn't like the ghost notes it produced diminished fifths in the higher registers - check out the DrZ forum - lots of dis-satisfied customers - only good for one sound - Buddy Whittington loves it but that is about it.
bajaman

soulsonic · Post by **soulsonic** » 27 Jul 2007, 10:00

Is that supposed to be a Baxandall tone control setup? If so, why isn't the connection to the volume control taken from the wiper of the Treble control as is usually seen?

I like EF86 tubes, but it's hard to find decent ones any more. Alot of them tend to have microphonic issues. I have a couple nice-looking Amperex ones, I scrounged out of an old tape recorder, but I haven't had a chance to try them out yet - that's why I would like to tinker with a circuit like this one.

That seems strange that your friend would have issues with ghost notes. Is that something that would be an effect of the circuit or more something to do with the speakers? I always figured it was more something to do with the speakers. The amount of doping on the cone can usually tune those aspects of the sound.

bajaman · Post by **bajaman** » 27 Jul 2007, 12:06

No - it has more to do with the filtering apparently - many people have sent their Route 66 amps back to DrZ - sorry no details given - but, i suspect it has something to do with the filtercaps and or the 10k resistor mentioned previously, and no, it is not a baxandall control - the treble part is more like a guitar treble cut type - EF86 has heaps more gain than a single 12AX7 section too.
bajaman

JHS · Post by **JHS** » 28 Jul 2007, 12:54

Due to the EF86 it's kind of HiFi-sounding, replacing the EF with something like the I-Stage from the Vibro King or '70-WEM Westminster will produce a more "rocksounding" amp.

Replacing the 47k in the phase-splitter with a 22k will produce a bit more grit at high Vol-levels.

JHS

bajaman · Post by **bajaman** » 28 Jul 2007, 13:38

You will need at least 2 stages to replace the EF86 though
bajaman

JHS · Post by **JHS** » 28 Jul 2007, 18:33

I have a better schem of the 66 with more info about the parts which I can't post her 'cos I don't have the permission. Absolut stunning is the quality of the parts used by Dr. Z, no cheap junk there, HiFi-highgrade through and through.

JHS

bajaman · Post by **bajaman** » 28 Jul 2007, 23:52

Aw shucks JHS
Yes I agree that DrZ uses good quality parts - sprague orange drops - silver mica caps - metal film resistors - JJ filter caps?? - CTS pots etc etc.
I have seen one in the raw

BUT - you can always go to his website - he has low resolution pictures there for anyone to see what he puts inside his amps.
Cheers
bajaman

JHS · Post by **JHS** » 29 Jul 2007, 11:56

On the Z-site I only found an inside pic from the Ghia. Compared to the 66, the Ghia is build with much cheaper parts (esp. the electrolytics and coupling caps) to gain the low price.

JHS

bajaman · Post by **bajaman** » 29 Jul 2007, 12:10

That is weird
I have the Maz 18, the Mazerati, and the route 66 innards, which I downloaded 3 years ago. They are only small images - if you want them PM me
Cheers
Steve

DougH · Post by **DougH** » 20 Aug 2007, 18:39

soulsonic wrote:Is that supposed to be a Baxandall tone control setup? If so, why isn't the connection to the volume control taken from the wiper of the Treble control as is usually seen?

I like EF86 tubes, but it's hard to find decent ones any more. Alot of them tend to have microphonic issues. I have a couple nice-looking Amperex ones, I scrounged out of an old tape recorder, but I haven't had a chance to try them out yet - that's why I would like to tinker with a circuit like this one.

There's an old Ampeg tone control that is very similar to the Rt66. I can't remember the amp's model #, you'll have to scrounge. I suspect the '66 tone control may be derived from that, but I wouldn't know.

I just built a Vox AC15 derivative and used a JJ EF806, which is their current production EF86. It sounds very good and is not very microphonic.

I've heard some '66 sound clips and IMO I like the sound. Big, thick, midrangey blues tone- kind of a one-trick pony but a good trick IMO. But a pair of KT66's would be way too loud for me. I'm still looking for a low-wattage pair of beam tubes that would sound like KT66's but haven't seen anything yet...

m.alexander · Post by **m.alexander** » 30 Aug 2007, 16:44

I love my DIY RT66/KT45 (6550 tubes)

AL · Post by AL » 30 Aug 2007, 16:57

Just out of curiosity - why couldn't you build that with a single 12AX7 (instead of the EF86) and use a shared cathode and shared plate arrangement? Or is that going to put you in a MAZ/Ghia realm?

AL

vanessa · Post by **vanessa** » 30 Aug 2007, 19:11

AL wrote:Just out of curiosity - why couldn't you build that with a single 12AX7 (instead of the EF86) and use a shared cathode and shared plate arrangement? Or is that going to put you in a MAZ/Ghia realm?

AL

The EF86 is a high gain tube that has a very rich, chimey distortion. This arrangement is found on the early Vox AC30/4 and AC15's (and is part of the reason they are so collectible). They [EF86] are prone to be microphonic, tube failure and this design was dropped by Vox as a direct result of. They switched to a ECC83 (12AX7) soon after but the design was very clean and guitarists missed the breakup of the EF86 design so they eventually implemented the top boost design (actually a Gibson amp design) to get some of that original breakup back.
In this design (RT 66) judging by the way it is voiced, the PI and the lack of neg. feedback, I'm guessing this amp would be a fav of many a AC30 lover that wanted more volume.

AL · Post by AL » 30 Aug 2007, 19:47

Vanessa,

I'm aware of the Vox angle but the EF86 (while apparently having a different sound/feel) is only a single stage correct? By sharing the plate loads of a 12AX7 you would be using two stages and, for lack of a better word, adding a little "oomph" to the stage as compared to splitting the stage in two as is common in most amps... I think.

AL