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Post subject: Final BDRI Tube Tone Mods?
Posted: Mon Aug 01, 2011 5:47 pm
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That title makes sense, right? :lol:

What I mean to say is that I did another tube swap with my BDRI to see what the effect would be. Here is a brief history of tube swaps with this amp:

Stock - Groove Tubes 12AX7s in V1, V2, and V3 with Groove Tubes 6L6R (Sovtek 5881s) in V4/5, bias set at 70 mV at the Fender test point - Very sterile sounding with harsh mids.

Tube Mod #1 - JJ 12AX7 in V1, JJ 12AT7 in V2, balanced JJ 12AX7 in V3, JJ 6L6GCs in V4/5 biased at 80 mV at the Fender test point - Smoother sounding with cleaner mids. Lower gain makes controlling the overall volume a little easier. Still not exactly what I was looking for.

Tube Mod #2 - Philips JAN 5751 in V1, JJ 12AX7 in V2, balanced JJ 12AT7 in V3, JJ 6L6GCs in V4/5, biased at 85 mV at the Fender test point - Very nice Blues sound. Harshness almost completely gone. Further reduction in overall gain makes volume control super easy. Nice clean sound. Drive channel has lost almost all overdrive unless gain is cranked to max with humbuckers. That's Ok since I use a Fulltone FD-2M for grit.

Stock speaker replaced with Eminence Cannabis Rex, same tubes as #2 - Bingo! Very smooth with nice fat midrange. Clean highs, tight and solid lows. Slightly louder due to higher speaker efficiency. Fantastic sound.

Tube Mod #3 - Electro Harmonix 12AY7 in V1, JJ 12AX7 in V2, balanced JJ 12AX7 in V3, JJ 6L6GCs in V4/5, biased at 85 mV at the Fender test point - Gain dropped a little bit, enough that I was able to turn the volume up a few notches and well as boost the tone stack settings a little bit. Much more midrange, so much that I had to cut back on the Mid control a bit. Treble very smooth, bass still very tight and clean. Still using the C-R speaker.

So, which one sounds best? Well, it's definitely a toss up beween Mod #2 and Mod #3 (both with the Eminence CR). There is a noticable difference in sound. #2, while very smooth is definitely a little brighter than #3 on the high end while #3 has fatter mids. Right now I am leaning towards #3 as my preferred configuration, though either #2 or #3 (with the Eminence C-R) would be excellent choices. Even #2 without the C-R is better than #1 and way better than stock.

The only "anomoly" I have noticed with Mod #3 is that when switching the Standby switch to "On" after turning power on, there is a slight "burble" or "burp" through the speaker that wasn't there with Mod #2. Any ideas as to what the cause may be? It does not occur while playing or at turn off. I checked the tube solder joints carefully as the V1 socket is very tight fitting and it was tricky removing and replacing the tubes.

Gotta go now. Time to play my guitar. :D

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Mon Aug 01, 2011 6:56 pm
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Final? I dunno....... :lol: You should use hex and use an A instead of 10 when you get to the tenth tube mod, to save space as there are about 216 different combinations, just going by gain factors and three positions. Toss different brands into the mix and you could have thousands of combinations. :lol:

Could there be something about the very low-gain AY that could be causing the "burp". Easy enough to swap that one tube and see. :idea:

How does the drive channel sound with the AY in V1?

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Mon Aug 01, 2011 7:31 pm
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shimmilou wrote:
Final? I dunno....... :lol: You should use hex and use an A instead of 10 when you get to the tenth tube mod, to save space as there are about 216 different combinations, just going by gain factors and three positions. Toss different brands into the mix and you could have thousands of combinations. :lol:


You know what they say: The enemy of the engineer is "better". :lol:

shimmilou wrote:
Could there be something about the very low-gain AY that could be causing the "burp". Easy enough to swap that one tube and see. :idea:


Well, I've already done that by swapping the 12AY7 for the 5751. No "burp" with the 5751.

shimmilou wrote:
How does the drive channel sound with the AY in V1?


Very clean. It sounds great with humbuckers plugged into input #2. :D

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Tue Aug 02, 2011 9:29 pm
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Well, I found it necessary to drop back to tube mod #2 (Philips JAN 5751 in V1, JJ 12AX7 in V2, balanced JJ 12AT7 in V3) with the CR speaker. Turns out my turn-on "burble" was caused by the E-H 12AY7. It was also begining to make slight "popping" noises as the amp sat idle. :(

Since it was only an E-H tube and nothing fancy ($30 w/shipping), its not worth sending it back. I might try this again in the future with a better tube as I did like the tone with the 12AY7. Of course, the tone with the 5751 is nothing to sneeze at either. :D

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 6:17 am
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It may not be that any other brand of AY would be better than what you have, but that the lower gain tubes draw more current than a higher gain tube. Check the voltage at TP3, which is across the Cathode resistor of V1, and compare between the two tubes and see if the AY doesn't have a much higher voltage drop across this resistor than an AX. I know that an AU runs much hotter than an AX, you might notice a temperature difference in the AY as compared to an AX also.

The schematic for the BDRI shows about 2 volts at TP3, which is about 1 mA of current draw, and that seems about right for a 12AX7. I can't remember just how much current an AY draws, but I believe it will be significantly higher than an AX. So, with the different current draw, that means that the voltage at the Plate and Cathode will be different also. This might be what is causing the noise in your amp (you already know it's the tube, but maybe this is why). :idea: I really don't like to use a tube with a lower gain than an AT myself

I'm skipping ahead a few mods down the road for you. :lol:

Tube mod #AE:
V1 - 5751
V2 - 5751
V3 - 12AT7

Tube mod #AF
V1 - 5751
V2 - 12AT7
V3 - 12AT7

:?:

Heck, with all of the different gain factors of tubes that you already have, you could make a list of the different current draws of each tube for future reference. :idea:

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 8:26 am
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shimmilou wrote:
It may not be that any other brand of AY would be better than what you have, but that the lower gain tubes draw more current than a higher gain tube. Check the voltage at TP3, which is across the Cathode resistor of V1, and compare between the two tubes and see if the AY doesn't have a much higher voltage drop across this resistor than an AX. I know that an AU runs much hotter than an AX, you might notice a temperature difference in the AY as compared to an AX also.

The schematic for the BDRI shows about 2 volts at TP3, which is about 1 mA of current draw, and that seems about right for a 12AX7. I can't remember just how much current an AY draws, but I believe it will be significantly higher than an AX. So, with the different current draw, that means that the voltage at the Plate and Cathode will be different also. This might be what is causing the noise in your amp (you already know it's the tube, but maybe this is why). :idea: I really don't like to use a tube with a lower gain than an AT myself

I'm skipping ahead a few mods down the road for you. :lol:

Tube mod #AE:
V1 - 5751
V2 - 5751
V3 - 12AT7

Tube mod #AF
V1 - 5751
V2 - 12AT7
V3 - 12AT7

:?:

Heck, with all of the different gain factors of tubes that you already have, you could make a list of the different current draws of each tube for future reference. :idea:


Hi, shimmilou.

Interesting theory.

I've already swapped tubes back to Mod #2 and buttoned things up so I don't have a chance to measure anything right now. But I looked up some specs.

According to the RCA tube manual, the 12AX7 is rated at a max plate current of 1.2 mA @ 250 VDC while the 12AY7 is rated at 3.0 mA at 250 VDC. On the other hand, the 12AT7 has a max plate current of 10 mA at 250 VDC. The 5751 is rated at 1 mA max plate current at 250 VDC.

I did try at one point, a 12AT7 in V1. I did not like the tone (too sterile), but I don't remember any "burping" like with the E-H 12AY7.

For now I have decided to just stick with the 5751/12AX7/12AT7 combo as the tone is very good and the amp is much quieter and easier to control the volume than with three 12AX7s. But I might change my mind later. I guess one can't have too many vacuum tubes. :lol:

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 8:41 am
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Yep, I thought that engineers didn't know the meaning of the word "final" anyway, so to be expected. 8)

Tune in next week, same bat-time, same bat-channel... :lol:

BTW, it would be nice if amps had a hinged door on the back for just such occasions....with a lock for safety of course. :idea:

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 11:19 am
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shimmilou wrote:
Yep, I thought that engineers didn't know the meaning of the word "final" anyway, so to be expected. 8)

Tune in next week, same bat-time, same bat-channel... :lol:

BTW, it would be nice if amps had a hinged door on the back for just such occasions....with a lock for safety of course. :idea:


Yep. The enemy of the engineer is "I can make it better." Now if I could only play the guitar as well. :lol:

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 11:21 am
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Mebbe play more and mod less?

:mrgreen:

Arjay

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 11:53 am
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Retroverbial wrote:
Mebbe play more and mod less?

:mrgreen:

Arjay


:!: :shock: :lol:

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 8:03 pm
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bluesky636 wrote:
Well, I found it necessary to drop back to tube mod #2 (Philips JAN 5751 in V1, JJ 12AX7 in V2, balanced JJ 12AT7 in V3) with the CR speaker. Turns out my turn-on "burble" was caused by the E-H 12AY7. It was also begining to make slight "popping" noises as the amp sat idle. :(

Since it was only an E-H tube and nothing fancy ($30 w/shipping), its not worth sending it back. I might try this again in the future with a better tube as I did like the tone with the 12AY7. Of course, the tone with the 5751 is nothing to sneeze at either. :D


imho i like #2 mod in terms tube selection, could the burble and popping from the balanced jj 12ax7 in v3? i know you deduced the 12ay7 e-h, im just thinking phase inverter, 12ax7 increase gain, 12ay7 in v1 lower gain, since your essentially lowering gain in v1 and raising it in v3. maybe the amp doesnt like it..
before anyone scratches their head, :? , im kinda thinking outloud, i know probably wrong..

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Post subject: Re: Final BDRI Tube Tone Mods?
Posted: Wed Aug 03, 2011 8:18 pm
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bluesstrattone wrote:
bluesky636 wrote:
Well, I found it necessary to drop back to tube mod #2 (Philips JAN 5751 in V1, JJ 12AX7 in V2, balanced JJ 12AT7 in V3) with the CR speaker. Turns out my turn-on "burble" was caused by the E-H 12AY7. It was also begining to make slight "popping" noises as the amp sat idle. :(

Since it was only an E-H tube and nothing fancy ($30 w/shipping), its not worth sending it back. I might try this again in the future with a better tube as I did like the tone with the 12AY7. Of course, the tone with the 5751 is nothing to sneeze at either. :D


imho i like #2 mod in terms tube selection, could the burble and popping from the balanced jj 12ax7 in v3? i know you deduced the 12ay7 e-h, im just thinking phase inverter, 12ax7 increase gain, 12ay7 in v1 lower gain, since your essentially lowering gain in v1 and raising it in v3. maybe the amp doesnt like it..
before anyone scratches their head, :? , im kinda thinking outloud, i know probably wrong..


Doubtful.

Before settling on Mod #2, I briefly tried the 5751 in V1 with a 12AX7 in V2 and V3. No "burble" in that configuration.

I'm sticking with Mod #2. All I had to do was drop the volume down from "8" to "6" and drop the treble down from "8" to "7" (bass stayed at "6" and mid stayed at "5") and I am a happy camper. As Arjay said, its time to stop swapping tubes and play the guitar. :lol:

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