Dumbleator build...Help, please?

[dobbhill]

I built the appartatus into an old Sears tube amp chassis.

I used Funk's (Brandon) tutorial as somewhat of a guide for the power supply, and used a schematic posted by heisthl (Henry) for the circuit. I ended up with a little hum, probably layout and the chassis is not shielded properly (no bottom plate, yet), but was wondering if the hum was caused by the filaments runnning @ 7.42vac. Any cheap easy tricks to get that down to more respectable levels?? I could DC the filament with lots of parts, but I'm lazy.

Then there's the tone. I'm wondering if this thing is messing with the crystal lattice or the timing of the electrons..... It really changes the tone somewhat, the OD is fat and "furry" compared to bypass. I haven't got a grip on the cleans yet, but it seems to "diffuse" the sound, not necessarily in a bad way, just different. Could this be the effect of the 500p/220k filter in the return?

Just thinking out loud.
Thanks in advance for any suggestions about lowering the filament voltage.

D

[dogears]

Just a couple suggestions.... Sorry about no advice on the filament issue.

Remove the 10K series resistor. No need to add resistance which could alter the tone.

Raise the dropping resistor feeding the follower. Shoot for 260V on pin 1. Anything 25V or higher on pin 3 is plenty. Real deals have 250V or so on the follower. Stock drop is 100K. Try increasing the drop to at least 75K or so.

Increase bypass cap on the recovery amp to 47uf. All real deals I have seen have 47uf. Why not baseline the real deal circuit before altering things....

Tube brand matter a lot! Try several different brands. JJ is fine for me.

I built the appartatus into an old Sears tube amp chassis.

I used Funk's (Brandon) tutorial as somewhat of a guide for the power supply, and used a schematic posted by heisthl (Henry) for the circuit. I ended up with a little hum, probably layout and the chassis is not shielded properly (no bottom plate, yet), but was wondering if the hum was caused by the filaments runnning @ 7.42vac. Any cheap easy tricks to get that down to more respectable levels?? I could DC the filament with lots of parts, but I'm lazy.

Then there's the tone. I'm wondering if this thing is messing with the crystal lattice or the timing of the electrons..... It really changes the tone somewhat, the OD is fat and "furry" compared to bypass. I haven't got a grip on the cleans yet, but it seems to "diffuse" the sound, not necessarily in a bad way, just different. Could this be the effect of the 500p/220k filter in the return?

Just thinking out loud.
Thanks in advance for any suggestions about lowering the filament voltage.

D

[dobbhill]

Thanks for the quick tips!
Iron is warming....

I might try a 6v battery on the filaments just to see....

D

[Guitarman18]

Hi dobbhill,

I have to say this is a first for me, being able to answer a question that dogears couldn't help with.

Anyway, I had exactly the same issue with my D'lator build and someone showed me this link. Works perfectly and also had it endorsed by a local old tube guru.

http://www.tubecad.com/july2000/

Required series resistance => R = Vactual - Vdesired/ 2 x Ih .

Where Ih= total heater current draw. ie. 1 x 12AX7 = .3 A


7.42-6.3/.6= 1.8666666 Ohms. So a pair of 1.866 Ohm resistors in series with heaters required.


Hope this helps,

Paul.

[dobbhill]

Paul:
Thanks much. Now to go to the "pile" and create a couple of resistors....

0.3 amps x 1 2. volts = .336 watts, so 1/2watt resistors will do?

Just checking my math...

D

[dobbhill]

Been sniffin' solder.
1) Changed the drop to CF supply- Per Dogears- CF plate now @ 252vdc, grid @ 13.2v, cathode @ 28vdc.
Return side the same.
2) Removed 10k jumper....
3) added 1ohm/5watt resistors in series with each heater leg- now @ 6.57vac

Thanks much for the assistance....
So to see how she sounds........

D

[dobbhill]

The Apparatus does change the tone.
It really adds dimension to the OD. It does make the lower ranges "fluffy" and "furry" in a pleasant "horn-ish" kind of way. There is a bit of loss of low end definition on the cleans.
I did not put the "brite" cap on the return (per Hentry's schematic), and something is needed to bring the top end back up. The original had 2 switchable brite caps. As of now, I run the Send at about 12:00 and the Return at 1:00. Anyone care to share their experience as to preferences with these caps in addition to the brite cap on the Master Volume?
As of now, I have no brite on the Master, as I felt it was not needed and made the amp too tweaky between 10:00 and 2:00 on the master. FWIW, I play a Tele and Altec 417C's. I could put one back in, but I don't want to have to use the Dumbleator just to compensate for the extra top end, if that makes sense. I'd rather try to make the D'lator more transparent...

I use an Intellifex, in case anyone wonders.....

Thanks to all for your input and experience.

[dogears]

You may not want to hear this, but you need the master bright cap. I have extensively A/Bed using a transparent loop versus using a master bright cap and specific capacitance cables to and from the Dumbleator. Hands down, the latter wins. It adds a vocal quality that is totally missing from the transparent setup.

For the record, guys like RF get their sound this way. Try it!

The Apparatus does change the tone.
It really adds dimension to the OD. It does make the lower ranges "fluffy" and "furry" in a pleasant "horn-ish" kind of way. There is a bit of loss of low end definition on the cleans.
I did not put the "brite" cap on the return (per Hentry's schematic), and something is needed to bring the top end back up. The original had 2 switchable brite caps. As of now, I run the Send at about 12:00 and the Return at 1:00. Anyone care to share their experience as to preferences with these caps in addition to the brite cap on the Master Volume?
As of now, I have no brite on the Master, as I felt it was not needed and made the amp too tweaky between 10:00 and 2:00 on the master. FWIW, I play a Tele and Altec 417C's. I could put one back in, but I don't want to have to use the Dumbleator just to compensate for the extra top end, if that makes sense. I'd rather try to make the D'lator more transparent...

I use an Intellifex, in case anyone wonders.....

Thanks to all for your input and experience.

[dobbhill]

Scott:

Thanks for the quick tip and your generous gift of experience, as always!

I'm OK with adding a brite cap to the Master. Do you use the brite caps on the D'lator in addition to the cap on the Master, or not?
Has anyone played with that 500p cap on the return grid circuit: cap type (mic vs disc) and value?
D