found a chassis in my storage place :D

[talbany]

had a 25k so put that in...Didn't like what it to the amp..sort of sounded a bit anaemic with that in. I tried a different (alpha) master volume pot from the original NOS CTS J taper that was in there, perhaps helped a bit so that's stayed but otherwise Back to stock again...


One of those days

M

Just wondering?
What are your voltages on both plates and cathodes on the loop?

[norburybrook]

had a 25k so put that in...Didn't like what it to the amp..sort of sounded a bit anaemic with that in. I tried a different (alpha) master volume pot from the original NOS CTS J taper that was in there, perhaps helped a bit so that's stayed but otherwise Back to stock again...


One of those days

M

Just wondering?
What are your voltages on both plates and cathodes on the loop?

Tony,

I didn't d a full check. I had 28V on the pin that's supposed to be around 30v, so I thought that was OK and didn't check anything else. That was when I had the 1m-27k -1.8k resistor in there I've changed it to 1m-10K-1.5k now.

I've been playing it for the past couple of hours as I've got a rehearsal tomorrow and I've got it just on clean sounding like a tweed , so with my humbucker tele it will crunch very nicely with the volume on 10 and clean up around 7 and below. I was quite enjoying it actually. I recon I could use the map just like this, and use the FET boost to kick it into heavier OD. The drive isn't overloading the FX either so it's very usable.

It's sort of like having two choices of tubes for your OD. the regular one or using the loop tube and having the master and send controls acting like the OD entrance trim.

thinking abut it I recon you could make this as a great amp with just the regular 3 tubes and ditch the OD section.....

you'd only need 1 footswitch then for the FET, no PAB and no OD.

Hmmm maybe I've invented a new amp


M

[martin manning]

That’s a good question on the voltages. I assumed you would adjust the loop branch’s first dropping resistor to get about 350V on the first node, and the 100k would take the second node down to about 250. Sounds like you were pretty close based on the send buffer’s cathode voltage. I would have kept the 27k and 1k8.

[talbany]

had a 25k so put that in...Didn't like what it to the amp..sort of sounded a bit anaemic with that in. I tried a different (alpha) master volume pot from the original NOS CTS J taper that was in there, perhaps helped a bit so that's stayed but otherwise Back to stock again...


One of those days

M

Just wondering?
What are your voltages on both plates and cathodes on the loop?

Tony,

I didn't d a full check. I had 28V on the pin that's supposed to be around 30v, so I thought that was OK and didn't check anything else. That was when I had the 1m-27k -1.8k resistor in there I've changed it to 1m-10K-1.5k now.

I've been playing it for the past couple of hours as I've got a rehearsal tomorrow and I've got it just on clean sounding like a tweed , so with my humbucker tele it will crunch very nicely with the volume on 10 and clean up around 7 and below. I was quite enjoying it actually. I recon I could use the map just like this, and use the FET boost to kick it into heavier OD. The drive isn't overloading the FX either so it's very usable.

It's sort of like having two choices of tubes for your OD. the regular one or using the loop tube and having the master and send controls acting like the OD entrance trim.

thinking abut it I recon you could make this as a great amp with just the regular 3 tubes and ditch the OD section.....

you'd only need 1 footswitch then for the FET, no PAB and no OD.

Hmmm maybe I've invented a new amp


M

Marcus
All that sounds good? but! to me, it's just not acting as it should. Your clean channel should still be pretty clean with that loop in.?? Another word your loop should not be adding any overdrive to your clean channel if everything were functioning normally IMO>
If anything else it should make the amp punchier

Tony

[norburybrook]

Just wondering?
What are your voltages on both plates and cathodes on the loop?

Tony,

I didn't d a full check. I had 28V on the pin that's supposed to be around 30v, so I thought that was OK and didn't check anything else. That was when I had the 1m-27k -1.8k resistor in there I've changed it to 1m-10K-1.5k now.

I've been playing it for the past couple of hours as I've got a rehearsal tomorrow and I've got it just on clean sounding like a tweed , so with my humbucker tele it will crunch very nicely with the volume on 10 and clean up around 7 and below. I was quite enjoying it actually. I recon I could use the map just like this, and use the FET boost to kick it into heavier OD. The drive isn't overloading the FX either so it's very usable.

It's sort of like having two choices of tubes for your OD. the regular one or using the loop tube and having the master and send controls acting like the OD entrance trim.

thinking abut it I recon you could make this as a great amp with just the regular 3 tubes and ditch the OD section.....

you'd only need 1 footswitch then for the FET, no PAB and no OD.

Hmmm maybe I've invented a new amp


M

Marcus
All that sounds good? but! to me, it's just not acting as it should. Your clean channel should still be pretty clean with that loop in.?? Another word your loop should not be adding any overdrive to your clean channel if everything were functioning normally IMO>
If anything else it should make the amp punchier

Tony

Tony,

Thanks, the loop is definitely adding a gain stage.

everything is switching as it should, PAB is switching in and out, FET is working as it should and the OD is switching in and out with the separate masters doing as they should . HAve I gto a strange value somewhere in the loop circuit? at the moment it's exactly (I think) as the Normster layout on page 1. except for I DON'T the 0.001uF on the send as I presumed that was a bright cap as it's on a switch. I just have a 100pF on the return instead of the 270.

The Normster amp has regular P.I values I wonder if the second gen values mean the loop is overdriving the P.I. ? just a guess. Having thought though the AT 7 has less gain than a 12 AX7....hmmmm mind you that's output not input....


OK, so I'll do a full voltage check after my rehearsal tomorrow and see what that looks like, otherwise where is the extra gain coming from?


I've got a full high plate values for V1 NOS Ruby12AX7
Regular second gen for V2 with separate master volume JJ 12 AX7
Loop: JJ 12 AX7

P.I is Second gen with NOS 12 AT7

output 50w 2x EHX EL34''s biased at ~38mA for 450v plate voltage.


M

[norburybrook]

OK, quickly measured voltages before setting off to rehearsals.


V3 loop voltages 12 AX7 JJ tube

1: 237v
2: 7.6v
3: 12v I think if I put the 27k back it will be 27v
4:heater
5:heater
6: 233v
7: 0v ?
8: 1.6v
9: heater





M

[martin manning]

Recover stage looks fine. I'd still recommend switching back to 27k/1k8, though. The bias voltage on the CF looks high. Try measuring across the bias resistor (1k5 or 1k8) to confirm.

On the gain structure, if you have high-plate values on V1 then that will ripple through the rest of the amp.

[talbany]

OK, quickly measured voltages before setting off to rehearsals.


V3 loop voltages 12 AX7 JJ tube

1: 237v
2: 7.6v
3: 12v I think if I put the 27k back it will be 27v
4:heater
5:heater
6: 233v
7: 0v ?
8: 1.6v
9: heater





M

Marus
Real Dumbleators have 255V range on pin 1 of the cathode follower section and around 28 to 31 on pin 3 if you used a 27k/1k8 combo. 12V is way to low! and could be whats distorting your signal. If you are using a 10k there on Normsters layout it could be dropping too much voltage

Tony

[martin manning]

Measure loop branch power supply nodes.

[talbany]

BTW. If your loop branch voltage is a little off you can compensate this by changing the value of the 27K resistor (leave the 1.8k). You really want to shoot for 30V exactly on the CF. As this is a big part of the D-Lator sound.

Tony

[norburybrook]

BTW. If your loop branch voltage is a little off you can compensate this by changing the value of the 27K resistor (leave the 1.8k). You really want to shoot for 30V exactly on the CF. As this is a big part of the D-Lator sound.

Tony

Thanks Fellas I don't have a 1.8k I'll try make one by adding a 300R to the 1.5 and i'll drop the 27k back in there. perhaps a 33k will get me to 30v.

Should I be adjusting the dropping string to get nearer 250v from my 235, or is 235 close enough?

@Martin , yes the high plate might be adding something, but I'm sure there are plenty of people who've done a high plate with a loop no? Also the bias voltage , measure the voltage across the 1.5k resistor, do you mean two measurements one at each side, or probes on either side of the resistor?


Erwin told me he liked the sound of having a lower voltage on the CF, he has 15 I think and says it gives him a 'compression' he likes, perhaps that's what I'm hearing /feeling about the clean headroom.


I'll heat up the iron later.


M

[erwin_ve]

Marcus, in my build the loop cathode follower has the 1k5-10k combo.
Because the resistor combo is smaller you have lower voltage at the junction of these 2.
Mine has 15,5v on that spot which for that 1k5-10k combo is the sweet spot Imo.

Btw my 2nd gen hybrid with loop has plenty of headroom. I can put 8,5v pp in the phase inverter before clipping. But you need a scope and load box to measure.

[norburybrook]

Marcus, in my build the loop cathode follower has the 1k5-10k combo.
Because the resistor combo is smaller you have lower voltage at the junction of these 2.
Mine has 15,5v on that spot which for that 1k5-10k combo is the sweet spot Imo.

Btw my 2nd gen hybrid with loop has plenty of headroom. I can put 8,5v pp in the phase inverter before clipping. But you need a scope and load box to measure.

Erwin,

On clean if you have your volume, send, return and master all at 12 O 'Clock is that clean for you? on my amp with humbucker tele that will give me a nice crunchy tone, like a tweed that's pushed.


I can get clean but I have to turn the master and send down to 3 and then turn the return up to compensate.


M

[norburybrook]

OK, found a 27k and a 1.8k and its a lot better now. Voltages are up.

pin 1: 255v
pin 2: 13v
pin 3 : 28v

pin 6: 235v
pin 7: 0v
pin 8; 1.6v


Sound is clearer too. everything on 12 O 'clock now with a regular tele is clean

Tomorrow I'm going over to Alan Darby's and were putting the New Celestion 300 in I'm very intrigued by this speaker...fingers crossed it's good....4lb's

I'm not sure if you've ever heard of Quilter amps but they've been using this speaker in their combos.The Jazz guys really like it.

M

[erwin_ve]

Marcus, on.your settings: thats approximatly my loudest setting I play and it' s f@@#$g loud, but still clean. If your volume control pots have 30% taper I bet that that setting will distort the PI.