Tweaking My Low Plate Amp (007): Another Resistor Makeover

[ayan]

The story of 007, the 7th ODS type amp I built, is that it started its life back in 2007 as mostly a high plate Skyliner using all New Sensor Corporation Marshall type iron. It was my spare amp, I wasn’t paying much attention to it and there was someone who had expressed an interest in buying it. As it were, the buyer didn’t come through and I decided to turn it into a low plate type, kind of like a 124 but using 100K OD trimmer and pots. Over the years, I continued to modify the amp whenever I had the urge to do something with my soldering iron. I flipped the caps, I added and removed the HF trim a number of times, I tried a ton of bright caps on the master volume, etc. The amp became my favorite and I gigged it to death for about 12 years straight. I captured a couple of these modifications in the pictures, where it’s pretty easy to see what changed – there are a couple of subtle things that can also be seen if one looks carefully.

Amp_007_ Original 2006 Version.jpg

Amp_007_2012_Mod_01.JPG

Amp #7 Mod Sept 2019 Before.JPG

Just a short while ago, I decided 007 was also going to undergo a resistor makeover like its 102 brother. Below is a picture of the preamp board gutted, mostly to show all the crap that ends up on the board when you gut it. By that time I had already done all the work on the V1 and V2 preamp tube sockets, as well as on the front panel stuff. The last picture is the amp after the makeover.

Amp #7 Mod Sept 2019 Gutted.JPEG

Amp #7 Mod Sept 2019 Completed.JPEG

The resistor changes are the same as for 102, with the exception of the V1B output resistor which a KOA Speer CF, and the pre OD resistor which is a Draloric LCA0414. Both are subject to change as I should have a couple of different resistors to try in those spots within the next few days. The 102 amp ended up with a Piher in the pre OD slot and a Draloric LCA0414 at the V1B output.

So how does 007 sound? I just finished the work last night and only turned the amp on to make sure that everything worked, and to set the bias and balance the PI trimmer. I’ll be checking it out this evening and will be able to report later. However, as I already hinted at in another thread, I tested this guy along the way and it was starting to sound more and more like the 102. Which was somewhat surprising, as they use different circuits, and use a few different caps here and there. The 102 clone has a 715P mid cap, the rest are all 6PS ODs, and 007 has all 6PS caps except for the V2A and V2B output caps which are 220P ODs.

Gil

[jelle]

Oooh, I bet that sounds good!

[talbany]

Killer! All that bad boy needs now is an Iskra and a Q-Line
007 "Shakin not Stirred'

Resistor Mafia.

[ayan]

Killer! All that bad boy needs now is an Iskra and a Q-Line
007 "Shakin not Stirred'

Resistor Mafia.

And sure enough, the makeover is now complete. The two new resistors are in place, and they made a difference. The amp is still very similar to the 102, but squishier and with more compression. My smoothest amp ever, and probably the one I’d keep if I could only have one. This guy is done. Thanks once again to Jelle and Tony, without whom this would have not been possible.

Gil

[talbany]

Killer! All that bad boy needs now is an Iskra and a Q-Line
007 "Shakin not Stirred'

Resistor Mafia.

And sure enough, the makeover is now complete. The two new resistors are in place, and they made a difference. The amp is still very similar to the 102, but squishier and with more compression. My smoothest amp ever, and probably the one I’d keep if I could only have one. This guy is done. Thanks once again to Jelle and Tony, without whom this would have not been possible.

Gil

For all the years you have graciously given your knowledge to members on this forum when very little info was shared about Dumble amplifiers you did!. For that we are always grateful!
Enjoy your 2 new amplifiers and was an honor to be a small part of it! Jelle is the man!
BTW. Shout out to Charlie Wilson as well who also contributed
Tony

[Charlie Wilson]

Looks good. I bet it sounds good to. Like the #124 style cathode resistor combo. 1k for PI cathode? Also, have you tried flipping your mid cap around?
CW

[ayan]

Looks good. I bet it sounds good to. Like the #124 style cathode resistor combo. 1k for PI cathode? Also, have you tried flipping your mid cap around?
CW

Hey, Charlie. Yes, 1K on the PI as I don’t have an 820R of the right type for that spot. If I can get something good, I’ll swap the 1K out. I did the same thing in my 102 as well. As far as the mid cap, there were a couple of other things I was going to try on this amp, among them flipping a couple of caps and maybe even experimenting with another mid cap type, and maybe PI input cap as well. However, after replacing the pre OD and V2A output resistors the amp sounded so good I decided to leave it alone. At least for a while. Funny thing is that whereas the 102 amp sounded too boomy with a 6PS mid cap, the low plate one sounds balanced with it.

[talbany]

Looks good. I bet it sounds good to. Like the #124 style cathode resistor combo. 1k for PI cathode? Also, have you tried flipping your mid cap around?
CW

Hey, Charlie. Yes, 1K on the PI as I don’t have an 820R of the right type for that spot. If I can get something good, I’ll swap the 1K out. I did the same thing in my 102 as well. As far as the mid cap, there were a couple of other things I was going to try on this amp, among them flipping a couple of caps and maybe even experimenting with another mid cap type, and maybe PI input cap as well. However, after replacing the pre OD and V2A output resistors the amp sounded so good I decided to leave it alone. At least for a while. Funny thing is that whereas the 102 amp sounded too boomy with a 6PS mid cap, the low plate one sounds balanced with it.

My Low Plate sounds balanced (@12 noon) and has the "Different" reversed Mid cap. BUT! I have 25uF's on my cathodes on V1. Hummm??
It was a little boomy with the 6PS
Tony

[norburybrook]

Looks good. I bet it sounds good to. Like the #124 style cathode resistor combo. 1k for PI cathode? Also, have you tried flipping your mid cap around?
CW

Hey, Charlie. Yes, 1K on the PI as I don’t have an 820R of the right type for that spot. If I can get something good, I’ll swap the 1K out. I did the same thing in my 102 as well. As far as the mid cap, there were a couple of other things I was going to try on this amp, among them flipping a couple of caps and maybe even experimenting with another mid cap type, and maybe PI input cap as well. However, after replacing the pre OD and V2A output resistors the amp sounded so good I decided to leave it alone. At least for a while. Funny thing is that whereas the 102 amp sounded too boomy with a 6PS mid cap, the low plate one sounds balanced with it.

My Low Plate sounds balanced (@12 noon) and has the "Different" reversed Mid cap. BUT! I have 25uF's on my cathodes on V1. Hummm??
It was a little boomy with the 6PS
Tony

Tony, was that value through experimentation or from a particular amp? I know 25uF is the stock Fender value but Dumble low plate is usually 10uF isn't it?

More bass with the 25's


M

[mojotom]

Hey, Charlie. Yes, 1K on the PI as I don’t have an 820R of the right type for that spot. If I can get something good, I’ll swap the 1K out. I did the same thing in my 102 as well. As far as the mid cap, there were a couple of other things I was going to try on this amp, among them flipping a couple of caps and maybe even experimenting with another mid cap type, and maybe PI input cap as well. However, after replacing the pre OD and V2A output resistors the amp sounded so good I decided to leave it alone. At least for a while. Funny thing is that whereas the 102 amp sounded too boomy with a 6PS mid cap, the low plate one sounds balanced with it.

My Low Plate sounds balanced (@12 noon) and has the "Different" reversed Mid cap. BUT! I have 25uF's on my cathodes on V1. Hummm??
It was a little boomy with the 6PS
Tony

Tony, was that value through experimentation or from a particular amp? I know 25uF is the stock Fender value but Dumble low plate is usually 10uF isn't it?

More bass with the 25's


M

The amp Tony talked about is a Low Plate MM style amp and from pictures of the famous tan MM ODS and Tony Bruno Super 100 pictures (based on the tan ODS) that circuit use 25u on V1.


Thanks Ayan for the reports, very useful !!

[erwin_ve]

Whats up with the reversed mid cap? (I presume you are talking about the outer foil position?)

[talbany]

Hey, Charlie. Yes, 1K on the PI as I don’t have an 820R of the right type for that spot. If I can get something good, I’ll swap the 1K out. I did the same thing in my 102 as well. As far as the mid cap, there were a couple of other things I was going to try on this amp, among them flipping a couple of caps and maybe even experimenting with another mid cap type, and maybe PI input cap as well. However, after replacing the pre OD and V2A output resistors the amp sounded so good I decided to leave it alone. At least for a while. Funny thing is that whereas the 102 amp sounded too boomy with a 6PS mid cap, the low plate one sounds balanced with it.

My Low Plate sounds balanced (@12 noon) and has the "Different" reversed Mid cap. BUT! I have 25uF's on my cathodes on V1. Hummm??
It was a little boomy with the 6PS
Tony

Tony, was that value through experimentation or from a particular amp? I know 25uF is the stock Fender value but Dumble low plate is usually 10uF isn't it?

More bass with the 25's


M

Marcus Good Question!
Yes I know the 25's give me more bass. and Dumble used all kinds of different value bypass caps on his low plate amps 5-50uF I'll explain
Going through some various shots of other ODS's you will notice that Dumble likes to use the 715P's as a mid-cap. After the build I noticed that I had to set my mids up fairly high to get the amp better balanced along with rolling off the bass.I also noticed the lower mids were not as pronounced as I would have liked. Being predominantly a Strat player the low mids have got to be there otherwise the sound gets too thin especially in OD. So then I remembered Dumble using the 715 as the mid-cap so I thought I would give it a shot and so far this seems to have cured the issue. The low mid pop along with the added articulation there let me roll up the bass and back off the mid control hence the better balanced the amp turned out. So I guess you could say it was a Dumble approved experiment
Later I was told that Dumble didn't use the 715's on his low plate amps however in the picture below I honestly thought that he used a 715 along with the 25uF bypass in the amp which is the one I copied. Notice the size of the cap matches the same size 715P's he uses in other amps I have seen an 800V 715P Mid cap. So with all this being said It could be that my amp is different given I used the Iskras which are slightly darker sounding resistors than the ones Gil used in his amp and the Q-lines Dumble used in his amps so maybe the 715 is a bandaid. However I believe it's better to achieve the overall tone of the amp through the sound of the caps rather than the sound of the resistors.
I hope all of this makes some sense>

Midcap.jpg

BTW. Mid cap is NOT the Blue one
Tony

[talbany]

My Low Plate sounds balanced (@12 noon) and has the "Different" reversed Mid cap. BUT! I have 25uF's on my cathodes on V1. Hummm??
It was a little boomy with the 6PS
Tony

Tony, was that value through experimentation or from a particular amp? I know 25uF is the stock Fender value but Dumble low plate is usually 10uF isn't it?

More bass with the 25's


M

The amp Tony talked about is a Low Plate MM style amp and from pictures of the famous tan MM ODS and Tony Bruno Super 100 pictures (based on the tan ODS) that circuit use 25u on V1.


Thanks Ayan for the reports, very useful !!

Correct!

[norburybrook]

@tony, thanks for the explanation. I love your MM amp hence me asking, I'm almost tempted to have a go as I've really got to like the low plate 50w 2nd gen I've got and really liked the sound of your amp when i listened to the you tube vid you posted. I'm wary though that i'll just end up with another ODS amp that sounds 'slightly' different from the ones I have and I already have too much choice with 3!!


M

[talbany]

@tony, thanks for the explanation. I love your MM amp hence me asking, I'm almost tempted to have a go as I've really got to like the low plate 50w 2nd gen I've got and really liked the sound of your amp when i listened to the you tube vid you posted. I'm wary though that i'll just end up with another ODS amp that sounds 'slightly' different from the ones I have and I already have too much choice with 3!!


M

Marcus
I am humbled that you were inspired to build based on the clip. I hear ya I have 5 now. . All I can tell you is the MM build was an experiment on the whole parts debate to use either the exact parts Dumble used or parts that I auditioned and liked and it made a big difference similar to what Gil just went through.So that was my inspiration and am glad I did. The Music man decision was due to I had a music man power transformer on my bench collecting dust. Along the way and through the help of Charlie and Jelle turned out to be a fun build and a great learning experience. The Music man is a wonderful amp and recommend it highly
Let me know if I can help if you decide to build one!

Tony