Fender HRDX help needed

[allbutromeo]

I have an old Hot Rod Deluxe that I bought used some time ago. It developed an issue where the volume cuts out when playing then comes back. I thought it might have been a tube issue so I replaced and biased it with a set of 6l6s that I know are good, but the problem remains (although until it drops out the tungsol RIs sound great and start getting some really good breakup around 4 on the clean channel). So I guess my question is, does anyone have any ideas what may be causing this. I plan on taking it to a tech to fix, but like taking a car to a mechanic I like to know what may be wrong so I don't get screwed over.

 

[Chickenwings]

Re: Fender HRDX help needed

Those amps burn through screen resistors a lot. They can easily be upgraded to higher wattage ones that wont burn out.
also:
http://www.premierguitar.com/articles/Diagnosing_a_Distressed_Tube_Amp

 

[BrianS.]

Re: Fender HRDX help needed

There can also be an issue with a couple of resistors in the power supply section failing. These are "drop down" resistors that are used to set the rail voltages for the solid state components throughout the amp. The resistors in question get very hot and can burn out as well as melt their solder joints.

I've also seen lots of cracked solder joints throughout these amps.

 

[gordon_39422]

Re: Fender HRDX help needed

I used to gig with an HRDx and LOVED it! There was a website devoted to this amp created by Justin Holt as his senior class project in Electrical Engineering. The original site is no longer, but there are mirror sites. I will try to find it and share the link with you.

From that page, I learned a great deal about tube amps in general, but even more about the HRDx. Here are a few suggestions for mods that you may like:

Replace linear Volume, Drive, and Bass potentiometers with these: (This allows you to dial-in the setting you desire. Ever notice how the amp gets real loud from 1-3, but doesn't get much louder from 4-12?)
http://www.newoldsounds.com/index.php?main_page=product_info&products_id=10699

Replace cheap screen resistors with some of better quality.

Replace driver - I tried 2 different ones, other than stock. One was an Eminence Patriot Series Screaming Eagle, the other was a Jensen C12N. They both were an extreme improvement in tone over the stock! They were both at 50 watts so they each broke-up near Max Volume, but had such clear headroom! I didn't think the amp sounded all that bad, but once I tested the Screaming Eagle, it was like my amp was facing rearward before and someone turned it around!




As far as repair, I can't say what specifically is wrong, but I've experienced/repaired these faults at one time or another with success:

Burned-out Screen Resistor(s)
Bad solder joints - I went back over the entire PCB and re-wicked the joints
This falls under "Bad Solder Joint" but needs specific attention: The connectors for the ribbons need to be inspected and rewicked. (Had one fail during a gig!)

I think this is one of the best entry-level tube amps, ever! I love swapping stories with fellow owners, so hit me up if ya wanna talk HRDX!

Keep on Rockin in the Free World!

 

[allbutromeo]

Re: Fender HRDX help needed

Thanks for the info guys, I guess this is what happens when you buy a cheap used amp sometimes. At least I got a few years out of it before all of this I only paid $250 is for it and about $75 more getting a preamp tube socket replaced

 

[gordon_39422]

Re: Fender HRDX help needed

I found a zip file containing the info from Justin's website before it closed down. The files are compressed to make transfer more efficient, but once the have been unzipped, the pages are PDF's!

http://www.stratopastor.org.uk/strato/amps/hrdx/HRD file.zip

Enjoy!

EDIT: I just downloaded it, Scanned with no threats, unzipped, saved the files on my PC and opened each. There are no threats within these files.