Dumbleland Special 150w ser#009 Schematic

[rccolgan]

my understanding is the preamp is SSS #002 without reverb so I think Aaron's schematic is missing the v1b & v2b .22uf feedback loop and the 100ohm resistors as well.

edit: I just re-read the thread and this was already pointed out. We need a GitHub repository for this stuff

[beasleybodyshop]

So has someone built this thing yet and gonna share the goods or should we continue to pontificate?

Daddy needs some audio clips!

[rccolgan]

Hopefully over the winter I'll be tackling this. I even acquired an original 1960s PT to compare to a new production Hammond for voltages, etc.

[Eges]

Do we have a consensus/most practical way to implement the power supply for 520 Volt plate voltage without UL taps? Also would a Twin Reverb PT enough for that kind of high voltage?

[Roe]

Do we have a consensus/most practical way to implement the power supply for 520 Volt plate voltage without UL taps? Also would a Twin Reverb PT enough for that kind of high voltage?

- use a big power resistor instead of a choke
- the twin PT has too little current and voltage

[Guy77]

Do we have a consensus/most practical way to implement the power supply for 520 Volt plate voltage without UL taps? Also would a Twin Reverb PT enough for that kind of high voltage?

One of these Hammond 300 series Power Tranies should work for you 373HX / 373JX. Make sure chassis is at least 12 AWG and bend the knee's before lifting LOL

Cheers
G

[Eges]

Do we have a consensus/most practical way to implement the power supply for 520 Volt plate voltage without UL taps? Also would a Twin Reverb PT enough for that kind of high voltage?

One of these Hammond 300 series Power Tranies should work for you 373HX / 373JX. Make sure chassis is at least 12 AWG and bend the knee's before lifting LOL

Cheers
G

Thank you Roe and Guy! Btw I probably will use 2x6550 but I think keeping voltages the same won’t be an issue right?

Also would love to learn how two rock handles the high voltage issue with 2 chokes if possible

[Smitty]

Having recently acquired Taylor Cox's first Steel String Singer in the Mike Hartman chassis (beautiful chassis, cab and really nice build--thank you Taylor and Mike!!) I'm now on full-blown a Texas Flood jag. Trying to find the Jackson Browne Dumbleland tones to compare to my new-to-me SSS 005 without enduring a full build.

I'm using the information in this thread to modify an Ultra Linear Bassman 135. Essentially adding the 12BH7 driver stage and reconfiguring the phase inverter for 12AU7 operation. Foregoing the filters and accompanying recovery stage for now.

As I think about adding an inverting gain stage to the output section and feedback loop it dawned on me that if I don't change anything else I'll have positive feedback due to the additional inverting gain stage. If this were an older amp I'd just swap the green and black wires on the output jack and be done with it. This amp has a four and eight ohm tap and the wacky switching output jacks, though, so...

Also, is it me or does the schematic on the first post in this thread infer positive feedback? Has anyone built this amp? Forgive me if this has been discussed before. I did search...

Thank you to everyone who contributed to this wonderful information.

[martin manning]

There are several opportunities to reverse the phase of the feedback: The output jack as you mentioned, but with a multi-tap OT secondary that's out. The others are the OT primaries the power tube grids, and the PI outputs. The 009 schematic does not have positive feedback as long as the phases are properly connected.

[Smitty]

Thanks Martin. My plan was to swap the phases after the driver.

Dumbleland Output.JPG

[martin manning]

Anywhere you have flying leads you can exchange. Power tube grids is probably easier since the 100k grid leaks and the bias connection are likely to be on the PI board.

[Smitty]

That makes good sense. Thank you, Martin!

[Smitty]

IMG_1654.jpeg

IMG_1655.jpeg

[Smitty]

DLS PI And Driver.JPG

[Smitty]

This modded Bassman 135 is as close as I've ever come to Texas Flood tone--that includes my AN SSS (#005 circuit). I'm using a pair of EVM 12Ls and boosting the signal with a vintage MXR Microamp. Big, loud and majestic with a little bit of give when pushed. Like the SSS, though, there is nowhere to hide.

Driving a 6L6 output tube grid with the plate of a 12BH7 has a more compressed sound than the SSS 12AX7 direct coupled cathode, but it doesn't fall apart nearly as quickly as a 12AT7 LTPI without a driver. Baby bear's porridge--just right.

485V on the plates. Idling at 60% of plate dissipation (37mA).

12BH7 driver B+ 294V and plates at 233V. Dropping 12V across a shared 1K cathode resistor for 6mA per side.

12AU7 LTPI B+ 292V and plates at 245/239. Preamp tube plates at 157.

Thank you to all who contributed to the Dumbleland Special 150W speculation.

I'll try to get a clip up this weekend.

PS apparently these amps are still a bargain:

https://www.ebay.com/itm/335898895056

Bassman 135 eBay.JPG