#189 50W Bluesmaster(Ripper?) Photos

Dumble schematics, designs, pictures. Only members may post files here.

Moderators: pompeiisneaks, Colossal

User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by martin manning »

Why not just jump across the socket to connect to the first stage plate? Or even from the pin 6 plate to the pin 2 grid stopper at the terminal strip? Retaining the grid stop at the "standard" value is odd too, as a large grid stopper on a less-than-unity gain CF doesn't do much for HF roll-off. It just seems very un-Dumble-like to me. :^/
chris_sanford
Posts: 131
Joined: Wed Feb 14, 2007 6:47 pm
Location: Portland, OR

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by chris_sanford »

martin manning wrote:Why not just jump across the socket to connect to the first stage plate? Or even from the pin 6 plate to the pin 2 grid stopper at the terminal strip? Retaining the grid stops at the "standard" values is odd too, as a large grid stopper on a CF doesn't do much for HF roll-off with its less-than-unity gain. It just seems very un-Dumble-like to me. :^/
Yes, the whole Marshall in a Dumble strikes me as very un-Dumble-like as well. I have not heard one of these amps in person though, so I will withhold judgement.

The grid-stopper on a CF will not lower the high-end as you say, but it will slow down the grid current, and that just might make the stage sound a little smoother under heavy over-drive conditions.

Even without the grid-stopper, using the connections on the tube socket would make it obvious to anyone that a CF stage was being used, so maybe the real purpose of that wiring scheme is obfuscation? :)

Another non-invasive test for the presence of a CF would be to check the signal phase at the loop jacks. Just a thought.

chris
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by martin manning »

You could also measure the stage gain to detect the presence of a CF. Just need someone who can get their hands on one of these.
splgeo
Posts: 97
Joined: Fri May 23, 2014 1:44 am

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by splgeo »

is it possible that the v2b resistor is 150 and not 150k? hard to tell.. if so could this be an AC coupled CF?
User avatar
UltraHookedOnPhonix
Posts: 414
Joined: Thu Dec 15, 2005 9:32 pm
Location: Dumbleland

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by UltraHookedOnPhonix »

splgeo wrote:is it possible that the v2b resistor is 150 and not 150k? hard to tell.. if so could this be an AC coupled CF?
You're right!

brown-green-black-black-brown-red is 150R, no questions! Ain't no way that second black band is orange in #189, which would make it a 150K.

Check out the two 150R virtual ground resistors HAD used in this pic (also courtesy of Charlie Wilson). Surprise, surprise... :wink:
You do not have the required permissions to view the files attached to this post.
Last edited by UltraHookedOnPhonix on Tue Jun 30, 2015 1:41 pm, edited 1 time in total.
splgeo
Posts: 97
Joined: Fri May 23, 2014 1:44 am

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by splgeo »

so the question is why is it such a lower value the most other grid stoppers? the possibility is that there is a CF and using that low of a value is the help prevent oscillations

or the normal 69K is where the trimmer is. and that resistor is used to adjust the signal going into the stage and the tone stack is in-between the two stages....
most M style amp imo do not have enough gain to account for the tone coming out of an amp like LC uses. and would you think the routing of the plate and cathode wires would be different... there routed a certain way to help positive/negative feed back in the amp.... so would they be different for a CF stage?
User avatar
UltraHookedOnPhonix
Posts: 414
Joined: Thu Dec 15, 2005 9:32 pm
Location: Dumbleland

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by UltraHookedOnPhonix »

I'm inclined to agree with Chris Sanford. I really think this is a JCM800-style CF.

Here's what I'm thinking:

*The green wire from the OD relay, probably leads to a fairly standard "pre-OD network", connects to lug 3 of a drive pot located on the front panel and finally leads back from the wiper to a 68K grid resistor connected to V2's pin 7.

*The blue plate wire (pin 6) connects to a 100K plate resistor on the pre board where it also connects to the green wire (seen exiting where the OD entrance we're more familiar with, would come from). This in turn, leads to a 150 Ohm grid resistor going to pin 2.

*The brown plate lead from pin 1 would simply lead to the B+4 node on the board. Both cathodes resistors would then occupy the same locations on board as the usual cap/res combos.

I've attached a schematic of the proposed circuit. Please excuse the shabby drawing, it was just a quickie...

I'm convinced it's a CF.
You do not have the required permissions to view the files attached to this post.
splgeo
Posts: 97
Joined: Fri May 23, 2014 1:44 am

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by splgeo »

if you look at the pics here what I see.... two shielded wires leading out of the top of the pre board. one going to the drive pot the other going to the od-vol pot. the wiper of the drive pot goes to the 68.1K grid resistor of v2a. the od-vol wiper disappears and I believe going to the channel relay.

the two shielded wire at the top of the pre board are routed as if normal non-cf amp.. the one on the right goes to the drive pot, and the one on the left after the tone stack to the od-vol pot.

so could the drive pot be used as a trim... something just aren't adding up to me

could it be that the signal goes
relay>cf>hrm stack? volume> 2nd triode> drive> out... that kinda of how it looks to me
10thTx
Posts: 1863
Joined: Sat Dec 30, 2006 1:13 am

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by 10thTx »

I drew up a wild guess on LC's amp some yrs ago. I've never seen inside a Dumble amp. I have NO special knowledge of this. ( I only say that because I"ve been pm'd a few times asking if I knew some secrets which I don't).

Consider this to have LOTS of errors, but perhaps it could be a useful schematic to this discussion? I changed a few things from the original drawing/guess as a result of this thread.

There is an attached SCH version that one could use to modify to post their ideas. ExpressSCH is a free download and is very user friendly and intuitive.

As an FYI, I have used an "OD" channel like this CF version on several amps and liked it.

With respect, 10thtx
You do not have the required permissions to view the files attached to this post.
splgeo
Posts: 97
Joined: Fri May 23, 2014 1:44 am

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by splgeo »

something I want to point out of this pic that seems abit weird to me is that there appears to be two blue wire coming out to the clean/od relay.
I know on most relays you just jumper over the two spot you need to clean signal to be.... but why have two different wires? is it because them come from two different spot?
You do not have the required permissions to view the files attached to this post.
splgeo
Posts: 97
Joined: Fri May 23, 2014 1:44 am

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by splgeo »

also I wanted to point out in #234 it has the jazz cap. going to the pab relay too

something I just came across the jcm 4010 has a 4n7 cap same value cap in the r/j switch connected to the mid pot wiper and mid cap, to ground
http://www.drtube.com/schematics/marshall/4010prem.gif
You do not have the required permissions to view the files attached to this post.
User avatar
glasman
Posts: 1446
Joined: Wed Jan 19, 2005 10:37 pm
Location: Afton, MN (St Croix River Valley)
Contact:

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by glasman »

martin manning wrote:Yes, that's clearly the case, it's a variable lift. Note also the "jazz cap" usually connected from the R/J switch to ground is going through what is usually the PAB relay, and the common lugs on the R/J switch are joined. Something different going on there for sure.
Seeing that both the MID and Bass are lifted by that trimmer kind of amused me a bit. I did the same thing on my very early SOD amps to tame the damned boost circuit. I do the same thing today on all Bluesmaster style tone stacks I build (mini instead of MEGA boost).
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification

www.glaswerks.com
User avatar
glasman
Posts: 1446
Joined: Wed Jan 19, 2005 10:37 pm
Location: Afton, MN (St Croix River Valley)
Contact:

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by glasman »

ToneMerc wrote:
Charlie Wilson wrote: Mike, unfortunately on this one I didn't take any measurements. Yes the Skyliner tonestack crossed my mind but it definitely has a Bluesmaster PI. What the heck is this thing?
CW
Variabe pad for the PAB.

TM
+1. Definately a skyliner style stack. Would bet there is a .01 and .1 under the goo.

Anyone catch the value of the V2 grid resistors? 27K ? Had to tell.
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification

www.glaswerks.com
Duble
Posts: 43
Joined: Mon Dec 10, 2012 7:24 pm
Location: St. Louis, MO

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by Duble »

glasman wrote:Anyone catch the value of the V2 grid resistors? 27K ? Had to tell.
Looks like 68k/150R no?
User avatar
glasman
Posts: 1446
Joined: Wed Jan 19, 2005 10:37 pm
Location: Afton, MN (St Croix River Valley)
Contact:

Re: #189 50W Bluesmaster(Ripper?) Photos

Post by glasman »

Duble wrote:
glasman wrote:Anyone catch the value of the V2 grid resistors? 27K ? Had to tell.
Looks like 68k/150R no?

I was referring to this picture. I don't see a 68K, looks like a 3?K or 2?k

But it might be a 68/150K pair, went back and took a second look.

http://ampgarage.com/forum/download/file.php?id=40819
Located in the St Croix River Valley- Afton, MN
About 5 miles south of I-94
aka K0GWA, K0 Glas Werks Amplification

www.glaswerks.com
Post Reply