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Post subject: HRD has lost its Drive and More Drive
Posted: Wed May 08, 2013 5:35 pm
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Aspiring Musician
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Today I noticed that my HRD has lost both its Drive and More Drive channels. Even with the Drive on 12, and Master cranked, the sound is loud but still "clean". This happens with both inputs.

My first thought is the usual culprits: the tubes. The power tubes are stock, but I've swapped the pre-amp tubes and currently running with a 5751 in V1, a 12AX7 in V2, and a Mullard 12AT7 in V3. I have a spare 5751 so I'll try that in V2 but was wondering if there's anything else I can try.

Thanks & Cheers!
BM

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Wed May 08, 2013 7:54 pm
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You have an op-amp problem in the channel-switching circuit. Swapping tubes will be of absolutely no use. Likely, concrete resistors R78 and R79 are the culprit (this notorious issue is well-known to FMIC and its warranty service centers).

Arjay

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Wed May 08, 2013 9:08 pm
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+1 Retroverbial

More specifically, the solder joints and/or circuit traces for the resistors are the most likely suspects.

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Thu May 09, 2013 4:36 am
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Thank-you gentlemen for the prompt and explicative replies.

I've had this HRD just over a year now and this is the third issue. Hopefully three will be the proverbial charm but I see Arjay shaking his head which suggests that this is not the end and more QC issues may follow. :cry:

I'll post back after I get the report from the FMIC authorized amp tech.

Cheers!
BM

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Thu May 09, 2013 9:18 am
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I was set to take the amp in for servicing then just for grins and giggles I decided to swap out the 12AX7 in V2 and for a brand new 5751.

As I was removing the 12AX7 I got the impression that the tube was not seated properly because it seemed a little higher than the 5751 in V1. Anyhow I made sure that the replacement 5751 was seated nice and snugly, turned on the amp, and voilà, the Drive and More Drive channels were back to normal.

This suggested a faulty 12AX7 in V2 but the seating issue was gnawing at me so I put back the same 12AX7 in V2 and everything with the drive channels was normal.

I don't think this rules out Arjay's suggestion about a problem with the channel-switching circuit but is it possible that a badly seated tube in V2 can have this kind of effect on the Drive channel?

Cheers!
BM

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Thu May 09, 2013 10:10 am
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Bluer Monkey wrote:
Hopefully three will be the proverbial charm but I see Arjay shaking his head which suggests that this is not the end and more QC issues may follow.


:lol:

Hopefully, re-seating your V2 tube has rectified the channel-switching issue but I still think it'd be prudent to examine the entire chassis for any developing problems that may surface down the road.

"An ounce of prevention......"

Arjay

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Thu May 09, 2013 11:29 am
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Half of V2 is used only for the drive/more drive channel, so that could very well be it. This is also consistent with poor solder joints, sometimes working, sometimes not. I hope that it is solved.

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Thu May 09, 2013 12:02 pm
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Re-seating the tube has "rectified" the situation with the Drive channel but I fear that the problem may not be entirely resolved.

Arjay, you're right about the proverbial ounce of prevention but in this case I think it applies only to people like yourself who know what they're doing. Even if I could identify a faulty solder joint or circuit tracer I wouldn't attempt to repair it so my only options would be to [a] pay a qualified tech for an ounce of prevention or [b] hope it fails while under warranty and let FMIC pay him the pound of cure. :lol:

Cheers!
BM

    Edit: ... about an hour later ...
      Well that was short-lived. We've lost the Drive channel again and no amount of seating, jiggling, and wiggling is working this time. Amp is going in for servicing. Stay tuned. BM.

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Thu May 09, 2013 1:32 pm
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Bluer Monkey wrote:
Re-seating the tube has "rectified" the situation with the Drive channel but I fear that the problem may not be entirely resolved.

Arjay, you're right about the proverbial ounce of prevention but in this case I think it applies only to people like yourself who know what they're doing. Even if I could identify a faulty solder joint or circuit tracer I wouldn't attempt to repair it so my only options would be to [a] pay a qualified tech for an ounce of prevention or [b] hope it fails while under warranty and let FMIC pay him the pound of cure. :lol:

Cheers!
BM

    Edit: ... about an hour later ...
      Well that was short-lived. We've lost the Drive channel again and no amount of seating, jiggling, and wiggling is working this time. Amp is going in for servicing. Stay tuned. BM.


I feel a great disturbance in 'the force'.

:(

Arjay

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Fri May 10, 2013 4:00 am
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Bluer Monkey,

You might to try the ancient "Wooden Chopstick" test.

One word of caution: The amp will need to be pulled from the cabinet and be "hot." So, if you are not comfortable with many hundreds of volts and the consquence, you may want to seek that tech.

With chassis pulled & on bench --- speaker(s) connected and no input, lightly tap each component and solder point with a wooden chopstick. Keep your free hand off the chassis. You should hear a tapping or static noise when you hit the faulty part or solder point.

Good luck, either way.


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Post subject: !
Posted: Sat May 11, 2013 5:40 am
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BMW2002Ti wrote:
Bluer Monkey, You might to try the ancient "Wooden Chopstick" test.
    :shock:
      :shock:
        :shock:
          Thanks for the suggestion, BMW2002Ti but Arjay, Bill, and shimmilou have successfully indoctrinated me with the fear of the dark side of the force lurking inside a tube amp. :lol:

          I'll be taking my HRD to a qualified and FMIC approved tech later today.

          Cheers!
          BM

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Sat May 11, 2013 8:29 am
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The newer the amp, the darker that "side of the force".

The old Fender's were so easy to diagnose and repair that even some hayseed hick with a three-day hangover could fix it while bouncing around in the back of a non-airconditioned tour bus whilst simultaneously composing a tears-in-your-beer C&W anthem using only a Schrade pocketknife and parts bought at a Winn-Dixie.

:lol:

Arjay

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Sat May 11, 2013 9:16 am
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Bluer, no on has bothered to point out to you that even once you get the problem solved, the tubes you are using will result in less overdrive in the drive and more drive channels than the factory installed 12AX7s that come in all three preamp positions. The 5751 and 12AT7 have less gain (gain factors of about 70 for the 5751 and 60 for the 12AT7) vs the 12AX7 (gain factor of 100). This may be the sound you are looking for, but just keep that in mind once you get the amp fixed. :wink:

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Sat May 11, 2013 9:53 am
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Retroverbial wrote:
...The old Fender's were so easy to diagnose and repair that even some hayseed hick with a three-day hangover could fix it while bouncing around in the back of a non-airconditioned tour bus whilst simultaneously composing a tears-in-your-beer C&W anthem using only a Schrade pocketknife and parts bought at a Winn-Dixie.
:lol: Arjay
    Wow! Arjay, your description is so vivid that I can actually picture this scene. ... It's a little scary, but I can see it. :lol:

bluesky636 wrote:
Bluer, no on has bothered to point out to you that even once you get the problem solved, the tubes you are using will result in less overdrive in the drive and more drive channels than the factory installed 12AX7s that come in all three preamp positions. The 5751 and 12AT7 have less gain (gain factors of about 70 for the 5751 and 60 for the 12AT7) vs the 12AX7 (gain factor of 100). This may be the sound you are looking for, but just keep that in mind once you get the amp fixed. :wink:
    Thanks, Bill. I am aware of this as it came up in a previous thread when I was asking for recommendations on how to quiet the beast. The lower gain tubes as well as using Input 2 did the trick and gave me a Bluesier crunch on the OD channel. I also like the 12AX7 in V2 so I'll probably use that once the current issue is resolved.

    My concern is with the reliability of my HRD and new Fender amps in general. I was considering the SS-22 then did a search and had second thoughts. The BJr is another possibility but I'm not entirely convinced. ... Anyhow, I'll leave this for another thread.

    Cheers!
    BM

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Post subject: Re: HRD has lost its Drive and More Drive
Posted: Sat May 11, 2013 11:15 am
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Bluer Monkey wrote:
bluesky636 wrote:
Bluer, no on has bothered to point out to you that even once you get the problem solved, the tubes you are using will result in less overdrive in the drive and more drive channels than the factory installed 12AX7s that come in all three preamp positions. The 5751 and 12AT7 have less gain (gain factors of about 70 for the 5751 and 60 for the 12AT7) vs the 12AX7 (gain factor of 100). This may be the sound you are looking for, but just keep that in mind once you get the amp fixed. :wink:
    Thanks, Bill. I am aware of this as it came up in a previous thread when I was asking for recommendations on how to quiet the beast. The lower gain tubes as well as using Input 2 did the trick and gave me a Bluesier crunch on the OD channel. I also like the 12AX7 in V2 so I'll probably use that once the current issue is resolved.

    My concern is with the reliability of my HRD and new Fender amps in general. I was considering the SS-22 then did a search and had second thoughts. The BJr is another possibility but I'm not entirely convinced. ... Anyhow, I'll leave this for another thread.

    Cheers!
    BM


Ok. Just wanted to make sure you were clear on the gain differences. :D

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