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beginner forum: for novice and developing blues harp players >
My hot rod Deville 410
My hot rod Deville 410
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SuperBee
4542 posts
Feb 26, 2017
3:35 AM
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This is my big amp, for stage work. It's s 60 watt amp with 4 x 10" speakers.
Believe it or not, sometimes i struggle to hear it on stage.
Am I just cursed with loud drummers and busy guitarists? Maybe.
The amp has been somewhat modified. It's got a 4.7k input impedance in input number 1, and a number of other mods.
The power tube bias was set very cold.
This means it tends to break up fairly early. Over the last few months I've begun to think it is set too cold so today I opened it up and reset the bias.
I believe the factory setting is around 30mA per tube. Mine was set closer to 15
these amps have a bias test point and adjustable bias pot, so it was relatively easy to adjust.
I decided to go with 21mA per tube.
I also replaced the PI (v3) with a12at7 tube.
I'd been running a 5751 in V1, but today I replaced it with s good 12 ax7.
Not the best idea to mess with your amp an hour before a gig, but my hunch was right. I got a tighter sound and more sweep on the volume control.
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SuperBee
4545 posts
Feb 26, 2017
1:20 PM
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These amps are pretty easy to adjust bias on. There's a test point on the circuit board and a trim pot you can adjust with a screwdriver as you watch the multimeter. I found a straightforward YouTube video which was very clear on the process.
Mine had been set at pretty much the lowest setting available and I had been thinking it was just a bit too loose. I might even set it a bit hotter again. Basically as it gets hotter the point where the amp breaks up gets louder. I mean, that's overly simplistic and electronically it's not a very good description but in the case of this amp it's pretty much the practical issue.
When I had this amp modded, I hadn't done any work on amps. So I researched online and gave instructions to the technician who did the work. I'm now reviewing those mods from a slightly more informed view. For instance, the higher impedance input mod I think only affects input number 1. Which is probably why my crystal mic was behaving differently at times with the amp and my Lone Wolf pedals, leading to my confusion about the impact of the pedal switched off. It's possible I was sometimes plugging into the high impedance input with the pedal switched off and other times plugging the mic direct into input 2, the lower impedance input. Possible, but also possible I'm making excuses for perception bias.
I also messed with settings yesterday. I tried cutting the mid entirely and running a bit more bass, cutting the presence. I liked it. I used the crystal mic for the entire gig, and used the LW reverb pedal instead of the reverb tank in the amp. This just made it easier to switch between effects, switch reverb off without having to visit the amp.
I ran my LW Octave pedal as a boost for solos. I set the volume to be a bit louder than my normal level so I could just step on it to come up whennthe mix was loud.
I'm glad I bought a multi-outlet power supply, which has at last made on-stage use of my pedals practical. Next trick is to build a board to keep them organised.
I have 4 now, and now that I've worked out why use of the reverb pedal is handy, I'll keep using it.
The Octave is mainly a boost although it's also a bit anti-feedback and it fattens thevsound. It's a fairly interesting pedal I think, worth playing around with, more than meets the eye. ThecDelay is just delay, on or off depending on the song. I used to have it on 90% of the time. I still like it a lot.
The LW reverb is a simple unit and works well. Reverb is my default sound pretty much. Used to be delay, but even then I was setting the delay to be somewhat reverb-like, very short intervals and short repeats. Now I run reverb and use the delay for a bit more atmospheric stuff.
My 4th pedal is rarely used but I'll put it on my board and put it in sometimes. It's an mxr univibe and with care can generate a useable organ kind of sound. But it's scary, easy to get 'too much' and sound ridiculous and mechanical, distracting.
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SuperBee
4550 posts
Feb 28, 2017
2:43 AM
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The Mods:
1. I mentioned above, R3 has been changed from 1 meg to 4.7 meg. This is the input impedance resistor and the change makes the amp suitable for use with a crystal mic. If one only plays dynamic mics, there's no call for this mod.
I also incorrectly stated above that this affects only input number 1. No, I looked at the schematic and it affects both inputs
2. C1, the cathode bypass cap on the first preamp stage, has been changed from 47 uF to 220uF. It's possible this might allow more bass to pass, but I haven't done a comparison and it seems to me that 47uF was already pretty big. But more bass was the intention. Maybe 'less of a treble boost' is another way to look at it.
3. R9 has been increased from 220k to 450k. The intention here is to tame the volume control and allow more sweep, making the volume a more even and controllable adjustment. The stock amps, especially pre 2013 (mine is 1997, pre-Mexican) were notorious for a very steep taper on the volume, making it quite difficult to get finecadjustment in the lower part of the scale.
4. R75 has been increased. This is the preamp drop resistor, which determines the voltage going to the preamp plates. The stock value is 10k, which delivers 380-ish volts to the preamp. My amp has a larger value to reduce the preamp voltage significantly. The concept is that the sound will be darker, less gain, less headroom (the amp has plenty and in stock form is inclined to feedback before breakup). We were aiming for 170-ish volts on the pin 1 of V1. I have forgotten the value of the resistor used at R75, but at least 56k. And 3watt. Really, it's the result that matters.
5. The preamp plate load resistors R4 and R11 were increased from 100k to 120k. This is a change borrowed from Aki Kumar's HRD, and it's perhaps not really called for in my amp. It actually has the effect of increasing gain but also perhaps affecting tone. The increased gain might seem like a bad idea, but remember we dropped the voltage which would have also reduced the gain some. But also, Aki's amp had a tube swap in V1, from the stock 12AX7 to a much lower gain 12AU7, so the gain increase was probably no issue. Aki did not have the reduced voltage mod.
My amp still runs a 12AX7 in V1, so this change to the load resistors may be redundant. They are big resistors, 1 watt I believe.
6. My power tubes have been biased very cold, to break up early. It's a compressed sound, breaks up quite early. A little too early for me so I have reset the bias. It's still way cold but warmer than it was.
7. My speakers have been rewired and I am using the 2 ohm tap from the output transformer (it also has an 8ohm tap, which is the stock arrangement). I'm not sure how much difference this makes, but there was an opinion it was a better arrangement for harp.
The vast majority of these mods were suggested by Mark Burness, who posts on MBH as 5F6H.
Last Edited by SuperBee on Feb 28, 2017 2:50 AM
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SuperBee
4551 posts
Feb 28, 2017
2:57 AM
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Aki Kumar has one of these amps which has been modified somewhat less.
The simple version is to swap V1 for a 12au7, and swap v3 to a 12 AT 7
Do the same mod as my mod number 1, and my mod number 5.
Also, upgrade the v3 plate resistors to 1 watt or higher cement types. This should prevent burnout from the higher current demands of the V1 and v3 substitutions. (I forgot to mention I also made this change, as these v3 plate resistors are dodgy even in a stock amp: I'm also running a 12AT7 in v3 at the moment, and I like it)
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SuperBee
4552 posts
Feb 28, 2017
3:06 AM
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Why would you do it?
If you need a big amp, these are plentiful, relatively cheap, still available new, and loud af.
The mods are not difficult and only require cheap parts.
The downside is the amps are somewhat of a pain to work on. And the construction is not that robust, likevthe blues jr, pro jr, hotrod deluxe.
But, mine is 20 years old and doing the job. The valve sockets are fine, despite the inherent weaknesses of soldering direct to the pcb. Likewise the input jacks are still good despite the fact they are also directly attached and cheap pieces.
Speakers are good, I suspect eminence legends, and the circuit works well (though note comments about plate load resistors). If you stay clear of the drive and extra drive channels, it's a pretty good sounding unit.
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MindTheGap
2183 posts
Mar 01, 2017
11:13 PM
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Excellent - so what does it sound like!!!??? Can we have some samples with this new bias?
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SuperBee
4557 posts
Mar 02, 2017
1:58 AM
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I don't have any recordings from the weekend. But I'm not sure if the difference is something you'd really pick up without an A:B demonstration (or an a:b:c etc)
I think the difference from the changing power tube bias is nicely demonstrated in dave Barrett's 'the bassman chronicles' under his 'equipment' section on bluesharmonica.com
When the bias is set very cold, the amp will sound quieter at the same volume setting than when the bias is hot. But then when you turn up to get the same loudness, the character of sound will be different.
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SuperBee
4561 posts
Mar 03, 2017
1:19 AM
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The Val King approach to mod the HRD is simpler.
Replace 5 resistors:
R3 to 4.7M
R4 and R11 to 120k, 1/2 watt
Upgrade the plate resistors on V3 to 1 watt types
Swap V1 to a 12AU7
Swap V3 to a 12AT7
Now I want to get another one and do this, I'd settle for a hot rod deluxe; same mods
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