It had to happen, but I've got to build another amp
So, I've decided on the earlier Dumble amps. I'm going to have a go at a 2nd gen 50w combo.
Chassis arrived today.
DSC_1609.JPG
DSC_1608.JPG
Couple of questions/observations;
No voltage regulator for the relay...
The relay itself on the layout... I presume the connections are as per the layout just with a different orientation from later models, I will be using teh standard Omron relays as in previous builds. THe relay on the layout has the power on the side but I presume the other 6 pins are the same.
Footswitch has a 4 pin XLR but only 3 used..I presume a regular 3 pin XLR will be fine.
Only a pre out no pre in.....why? any reason not to have it like the later amps?
Marcus
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norburybrook wrote: ↑Tue Mar 06, 2018 7:20 pm
It had to happen, but I've got to build another amp
So, I've decided on the earlier Dumble amps. I'm going to have a go at a 2nd gen 50w combo.
Chassis arrived today.
DSC_1609.JPG
DSC_1608.JPG
Couple of questions/observations;
No voltage regulator for the relay...
The relay itself on the layout... I presume the connections are as per the layout just with a different orientation from later models, I will be using teh standard Omron relays as in previous builds. THe relay on the layout has the power on the side but I presume the other 6 pins are the same.
Footswitch has a 4 pin XLR but only 3 used..I presume a regular 3 pin XLR will be fine.
Only a pre out no pre in.....why? any reason not to have it like the later amps?
Marcus
I build one like it ten years ago with the same chassis.
I got to redrill a lot of holes to match the layout I've got at the time.
I like that circuit a lot. A bit hard to balance clean and OD and whether to use AT or AX PI tube.
I did use a classic style tonestack with deep and PAB on that one but you could use 40 or even 13 tonestack too.
Like to be opened volume wise. Awesome slide tone.
The amp like NOS pre and power tubes and I like it on a closed back speaker cab.
Tony Talbany was very helpful on this one. He build a 100w with 13 tonestack.
I did use a 10k pot between speakers out and feedback resistor (820R) to open up the amp a bit.
jam-mill wrote: ↑Wed Mar 07, 2018 12:16 am
Marcus,
I'll be anxious to hear how your build turns out as I proceed with the
similar/same 2nd generation choice for the Fender HRD conversion.
-jack
Jack I'm curious too, as it will be the first 'early' Dumble I'll have built. I'm hoping it will be a little less refined than the later ones, but who knows, I like the process so it's all good
Just getting a parts list together.
Only issue with th etransformers I've been using is the mounting holes dont fit as they're smaller so I have to make a mounting plate from alluminium to stop them dropping through the hole. I looked at Hammond again as they're standard mounting but was horrified how much the price had incresed over 3 years here in the UK, nearly doubled!!
So mounting plate it is then!
One thing I'm going to try this time is a suede covering. Been wanting to do that for a while and seeing Taylors recent offereings has inspired me. Burgundy suede with the wheat grill cloth
Can I ask about the relay and footswitch in this amp?
Is there any mileage in making boards up exactly as per the layout and using a 12v relay with no regulator....or doing it like I've done my other builds and use 6v relays with a regulator?
I 'm thinking for authenticity I should make it like the original. which I 'think' has a 6 v transformer and has the voltage doubled on the board and sending it straight to the relay without a regulator.
I also presume that the footswitch will be just half the regular one, complete with LED.
can anyone chime in with the difference between the 12AT7 and the 12 Ax7 for the PI
norburybrook wrote: ↑Fri Mar 09, 2018 8:51 pm
Right, getting my parts list together.
Can I ask about the relay and footswitch in this amp?
Is there any mileage in making boards up exactly as per the layout and using a 12v relay with no regulator....or doing it like I've done my other builds and use 6v relays with a regulator?
I 'm thinking for authenticity I should make it like the original. which I 'think' has a 6 v transformer and has the voltage doubled on the board and sending it straight to the relay without a regulator.
I also presume that the footswitch will be just half the regular one, complete with LED.
can anyone chime in with the difference between the 12AT7 and the 12 Ax7 for the PI
Marcus
For the 12v Vs regulated voltage doubled 6.3 volts, it only does the relay power on off, so has 0 impact on tone... IMO do what's simplest for you
norburybrook wrote: ↑Fri Mar 09, 2018 8:51 pm
Right, getting my parts list together.
Can I ask about the relay and footswitch in this amp?
Is there any mileage in making boards up exactly as per the layout and using a 12v relay with no regulator....or doing it like I've done my other builds and use 6v relays with a regulator?
I 'm thinking for authenticity I should make it like the original. which I 'think' has a 6 v transformer and has the voltage doubled on the board and sending it straight to the relay without a regulator.
I also presume that the footswitch will be just half the regular one, complete with LED.
can anyone chime in with the difference between the 12AT7 and the 12 Ax7 for the PI
Marcus
For me the AT was great for clean (more current) and the AX was best for OD but then clean was a bit flat.
You should try both.
I like the OD a lot and on my amp without mods the clean was hard to balance with the OD (no OD master) so I kept an AX. It does bring down the volume where the amp start to sing too.
I would start with the AT, choose between 13 and 40 stacks then tweak the amp if needed then have a try at the AX.
I did build my 70's to run 5V relays but I should have use 12V (never had an issue but I would use the same relay on all amps now just in case I need some spares).
Nowadays I use the rectifier tap with a doubler, without a regulator and got no issues. Led powered like a Marshall footswitch, simple two footswitches box with a stereo jack on chassis.
I built a hybrid #40 with a master for the OD channel and integrated Dumbleator. Footswitchable FET boost. Best Dumble circuit I've ever built for singelcoil pickups!
dbeasley wrote:I built a hybrid #40 with a master for the OD channel and integrated Dumbleator. Footswitchable FET boost. Best Dumble circuit I've ever built for singelcoil pickups!
Sent from my Moto G (4) using Tapatalk
Sounds interesting. I'd love to do an on board loop, I might look into it on this build. Did you put everything on the main board or hang stuff off terminal strips near the valve?
I am going to do a FET boost on this build for the first time, having it switchable sounds like a good idea...
Can I make two relays work with a 4 pin XLR socket? Can I use the case as a ground on each end using the shield from star quad cable like I have used on my other builds?
norburybrook wrote: ↑Fri Mar 09, 2018 8:51 pm
can anyone chime in with the difference between the 12AT7 and the 12 Ax7 for the PI
For me the AT was great for clean (more current) and the AX was best for OD but then clean was a bit flat.
You should try both.
I like the OD a lot and on my amp without mods the clean was hard to balance with the OD (no OD master) so I kept an AX. It does bring down the volume where the amp start to sing too.
I would start with the AT, choose between 13 and 40 stacks then tweak the amp if needed then have a try at the AX.
12AX7 gain 100
12AT7 gain 70
Here's a comparison chart, HC is heater current, Mu is gain
dbeasley wrote: ↑Sat Mar 17, 2018 6:01 am
I built a hybrid #40 with a master for the OD channel and integrated Dumbleator. Footswitchable FET boost. Best Dumble circuit I've ever built for singelcoil pickups!
Sent from my Moto G (4) using Tapatalk
I love mine too! Best sounding built with clean and overdrive for strat.
Marcus, a 4 pin cable is fine. I got mine with 5 pin but also have a pab.
On the PI: the values for the plates are designed to work with 12AT7. The Miller effect on a 12At7 is less so you got a little more highs. Also the Nfb resistor coming from the ot sec. is smaller(more Nfb!).
You might want to change that to 4k7 instead of a 3k3.
dbeasley wrote:I built a hybrid #40 with a master for the OD channel and integrated Dumbleator. Footswitchable FET boost. Best Dumble circuit I've ever built for singelcoil pickups!
Sent from my Moto G (4) using Tapatalk
Sounds interesting. I'd love to do an on board loop, I might look into it on this build. Did you put everything on the main board or hang stuff off terminal strips near the valve?
I am going to do a FET boost on this build for the first time, having it switchable sounds like a good idea...
Can I make two relays work with a 4 pin XLR socket? Can I use the case as a ground on each end using the shield from star quad cable like I have used on my other builds?
Marcus
Sent from my Nexus 6 using Tapatalk
Yes. One relay for the OD and one for the FET is fine. I ended up cobbling together a layout on the board for the D'lator. Also created a pair of filter nodes for it as well. Was quite a bit of extra work making it all jive - I think I tapped off the screen node and used a 32/32uf cap can. You can also use Quad cable no problem. One conductor for FET and OD respectively, shield for ground.
