Amp Issues

DeadAirMD

DeadAirMD

Well-known member
Hoping someone out there can lead me in the right direction, or any direction but the one I'm stuck with for that matter.

Problem amp is a 1st Gen. Fender Hot Rod Deluxe. A few months back I replace the about to explode 450/500v big boy capacitors. They were already erupting with gunk coming out the top and bottom of the caps. The amp sounded great after doing this, but unfortunately has drifted into the shit......big time.

I only use the Clean Channel and run a ton of effects through it. Everything clean sounds perfect, but as soon as I turn on any distortion/overdrive pedal, my amp sounds like it's squeezing out the sound. With distortion/overdrive, it always sounds like a cocked wah. Every single distortion/overdrive pedal sounds the exact same to each other. Every guitar single coil or humbucker, sounds the exact same. I replaced the speaker with an Eminence RW&B, didn't change anything. The EQ on the amp either makes the woofiness brighter or darker, but does nothing to change that single tone. I replaced all the tubes and I'm using (6L6, 12ay7, 12ax7, and 12at7). They did nothing. I rebiased the amp after replacing the tubes and that did nothing as well. Could one of the tubes possibly be bad?

I'm super bummed out because my amp sounds terrible and it's painful to listen to my recordings.

Here's some sound samples. All audio you hear is playing through the amp. Even with just the guitar, terrible. Please help 😢

https://soundcloud.com/dead-air-electric%2Fsample-1

https://soundcloud.com/dead-air-electric%2Fsample-2
 
I've got a call into a local amp guy, but he hasn't returned my calls yet. I have a ton of components for the amp and have the ability to fix it myself, I just know next to nothing about diagnosing amp Issues.

@PunchySunshine for testing, are there actual test pads like for the biasing to test at, or are you talking about using a MM on certain parts of components?


I guess either way, it will be helpful to have all possible information on diagnostics I run if I need someone else to fix this for me.
 
The test points are on the schematic labeled TP. For TP31 you would be able to get the value from any of the components connected at that node- R90, R89, or pin 5 of U3B


1706643646291.png
 
DeadAirMD said:
I've got a call into a local amp guy, but he hasn't returned my calls yet. I have a ton of components for the amp and have the ability to fix it myself, I just know next to nothing about diagnosing amp Issues.

@PunchySunshine for testing, are there actual test pads like for the biasing to test at, or are you talking about using a MM on certain parts of components?


I guess either way, it will be helpful to have all possible information on diagnostics I run if I need someone else to fix this for me.
Click to expand...
MM on certain parts in certain conditions. Just make sure to read all the notes on the schematic for settings and conditions of the amp for proper measurement. It's just like using an audio probe, except it's HIGH VOLTAGE. One arm behind the back or other safety precautions in place before poking around live tubes. I like to use multiple MMs with the hook attachments so I don't have to be anywhere near the insides while it's live. I'm not to be trusted with such things though!
 
@RetiredUnit1 was more than generous with his complete amp knowledge and was very kind when I reached out for help with replacing the caps. From that experience I'm definitely more than mindful about what I'm doing. I'm all about those hook attachments or alligator clips. Made the cap changing a breeze.

@PunchySunshine any tips on measuring the tubes? Just want to make sure they and their connections are working as they should. Will have to get numbers from their respective datasheets.
 
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DeadAirMD said:
@RetiredUnit1 was more than generous with his complete amp knowledge and was very kind when I reached out for help with replacing the caps. From that experience I'm definitely more than mindful about what I'm doing. I'm all about those hook attachments or alligator clips. Made the cap changing a breeze.

@PunchySunshine any tips on measuring the tubes? Just want to make sure they and their connections are working as they should. Will have to get numbers from their respective datasheets.
Click to expand...
@RetiredUnit1 is the man! I'm only on my third tube amp at this point so I'm a complete and total noob FWIW.
It was either Psionic or Uncle Doug I heard say "It usually not the tubes" at one point in his videos and I've taken that to heart. As long as I have a known good backup tube to try, I'm happy in that regard. I know the schematic test points are the best clues I've been using to be able to troubleshoot and modify so far. And I retract my earlier statement of starting with the power supply, start @ tp1 and just go up. I like to use a spreadsheet to keep track of all the data I collect. The test setup for your amp isn't bad at all. No test tone needed. I like to use a dummy load resistor on the speaker output so that I'm not tearing up the speaker and my ears..
If the tube sockets are loose, I feel like you'll know. They can be"massaged to fit tighter but changing them out isn't too terrible and if they're actually loose fitting, I would suggest it.
 
These amps are great amps, but they are definitely built to a price point, so do have a few known “gotchas”. Again not bashing, as I can’t think of a single amp that is any better built than these at that price point.
First thing before trying to suss out any problems is go to your local mega center and try one new with a common pedal you would use. Make sure it IS your amp and not that you simply don’t like the amp (although that can be addressed as well ;)

Some known issues:
1. They used “Illinois” branded electrolytic caps in the amp— not just the filters, but also bypass caps… in addition to changing the filter caps, bypass caps are also recommended
2. Jacks are notorious for getting dirty/gritty and need cleaned. Also if you can clean the switching contacts do that as well. While in a cleaning mode, won’t hurt to spray some deoxit in the pots as well as clean the tube sockets (plenty of videos on that)
3. Solder connections to the jacks are prone to cracking. Reflow them when inside.
4. PCBs are old school, thin, single sided boards, and can develop cracks and more frequently cold solder joints— especially around the tube sockets.
5. Board mounted tube sockets with little strain relief (see above)
6. Volume pot taper that goes from 0-60 all within the first 5° of rotation. Hard to dial in. A lot of folks throw a volume pedal or even a pot in the fx loop (fender labels it “line out” and “line in”. Throw a volume pedal or eq in the loop and cut the volume there while raising the built in amp volume to 3 or 4 and listen to it open up
7. Test all components around the power tubes, look for signs of burnt parts etc.

Above that I would do a “pop test” - measuring all voltages on tube pins working from output back to input, and hearing a progressively louder pop. Noting you should NEVER have a positive voltage on tube grids (power tubes will have negative voltage of course), any voltage on preamp tube grid is sign of bad coupling caps (not super common, but does happen)

PLEASE be sure of all safety concerns, keep safe and if you are the least bit unsure, take it to a reputable pro!
 
@PunchySunshine @Giorfida man, thanks for taking the time to run all of that down. It's hard to find a mostly complete synopsis in one location, so I really appreciate the time you took to write all that up.

I have a ton to work on this weekend, but I love doing stuff like this so I'm looking forward to it. Plus I might be able to fix my amp! I've had this for 20+ years and the past 12 months it started developing all sorts of issues. Just needs some tlc.

Great idea on keeping a spreadsheet on the numbers I collect!
 
DeadAirMD said:
@PunchySunshine @Giorfida man, thanks for taking the time to run all of that down. It's hard to find a mostly complete synopsis in one location, so I really appreciate the time you took to write all that up.

I have a ton to work on this weekend, but I love doing stuff like this so I'm looking forward to it. Plus I might be able to fix my amp! I've had this for 20+ years and the past 12 months it started developing all sorts of issues. Just needs some tlc.

Great idea on keeping a spreadsheet on the numbers I collect!
Click to expand...
If you have any questions along the way, don’t be afraid to post here or IM me. I’ll be glad to help. I started on amps a couple decades ago the same way you did!

@PunchySunshine definitely agree on most of that- it’s rarely the tubes. And I also agree a dummy load is good to protect speaker (except in the case of a dead amp… a cheap crappy speaker is preferred there to do a thorough pop test. But since his amp is alive, I agree the dummy speaker.
 
When you play clean, can you really push the volume through it? If it can play loud while clean, I’d recommend trying just your guitar, amp, and a single drive or distortion peddle, as a test.

I‘ve built amps, but can’t pretend to really understand what the electrons are up to. But it seems like if you get a good clean signal through it, and if it sounds bad with an extra drive attached, the new signal is overloading the input, creating more distortion than expected?

I also would replace all bypass caps (certainly EL ones) when the power caps need replacing, which yours obviously did.
 
I've used this amp the exact same way the entire time I've had it. Always use a looper and play over the top. The past few years I've majorly upgraded my setup and now I build a drum track on Ezdrummer, loop that, then play guitar over that. The sample audio clips I cut from live recordings of me playing through my Boss Rc300. Always sounded great never any issues.

Every clean sound, drums, bass, clean guitar, and any effect that isn't distortion/overdrive sounds perfect. As soon as I kick on OD for a solo, the tone just sounds atrocious. I've tried pedals I've built, pedals I've bought, all different settings on pedals and amp, everything sounds terrible no matter what I do. After testing everything from different guitars, pedals, cables, power sources..... I've determined it has to be the amp.

Going to record all my test results this weekend and will also replace the remaining caps and any problem components I may find. Did a quick inspection last weekend and just a basic visual check didn't turn up anything suspicious. Not like last time when the Illinois caps were literally erupting......
 
I know next to nothing about this amp, other than I have heard a lot of complaints.

I think the problem is in the name and the usage. 'Hot Rod' deluxe, as I'm looking at the input stage I see the bias is done with a 47uf 1.5k which is very unFenderIsh. And a 250k volume pot?

I think maybe this amp was built to be played wide open, not squeezed down to the clean section of the volume spectrum.

Try playing it with native distortion, i.e. turn it UP. It sounds very thin to my ears, like the signal needs to be stronger.

Well my stomach is growling, time for breakfast.....
 
Yeah definitely way better amps out there. This was my 1st amp 24yrs ago. The problem with native distortion is that I basically am playing a full band (drums, bass, keys, guitar) with my looping pedal, so I'm solely restricted to using dist/OD pedals since I can clip the rest of the "band".

I will be buying a new amp some time this year that better suits how I make/play my music. Some people have said a bass amp or keyboard amp.

Basically need to find an amp that can handle drum tracks, bass guitar, and guitar with tons of effects. A tall order no doubt.....

The cleans on this HRDX are incredible though and it has a tender spot in my heart.
 
DeadAirMD said:
Yeah definitely way better amps out there. This was my 1st amp 24yrs ago. The problem with native distortion is that I basically am playing a full band (drums, bass, keys, guitar) with my looping pedal, so I'm solely restricted to using dist/OD pedals since I can clip the rest of the "band".

I will be buying a new amp some time this year that better suits how I make/play my music. Some people have said a bass amp or keyboard amp.

Basically need to find an amp that can handle drum tracks, bass guitar, and guitar with tons of effects. A tall order no doubt.....

The cleans on this HRDX are incredible though and it has a tender spot in my heart.
Click to expand...
Mojotone makes a DR504 kit now. This is the Hiwatt that David Gilmore plays. I built one NOT from a kit back in 2008. There was a guy on the Vintage Amp forum that made the chassis and faceplates so I bought six from him. Sold three and it paid for the three I kept.

This amp sounds the same from 1% to 100% gain. Gilmore is a pedal man, and it's why he plays it. You can get speaker distortion at full volume, and that sounds like a monster roaring. Literally unscrews light bulbs. Hendrix used it on an AB/Y with his Marshall, so the Hiwatt was the clean part and the Marshall the gritty. It's how he achieved that clean/breakup sound.

It's $821 minus the price for the head cab which is sold separately, but that includes the tubes which can be quite pricey if purchased separately.

www.mojotone.com

Mojotone Custom 50 Guitar Tube Amp Kit

Amp Kit Difficulty LevelEasy HardIf this kit shows as out of stock please check here for more information.Please read our article 'Mojotone Amp Kit Building Primer' along with our amp kit disclaimer located in the Specs tab before buying this kit.The design was a labor of love that started in a...
www.mojotone.com www.mojotone.com
 
Just to clarify.....

To run checks on my MM on the test points, I have the amp powered up, on "stand by", ground the MM, and touch to the "Test Point" locations on the schematic?

I did this last night and was getting readings that were lower, but in the ballpark for what the TP's states. A few components (TP4) read OL.

Just want to make sure I'm recording these numbers accurately. I have all the parts, still undecided if I will replace any or take it to a tech. Still want to get some readings so if I go to a tech I have a better explanation to give.
 
DeadAirMD said:
Basically need to find an amp that can handle drum tracks, bass guitar, and guitar with tons of effects. A tall order no doubt.....
Click to expand...

Definitely not “cool” but these 90s fender full range things are cheap. Guy I jam with grabbed one for $100 and has been using it on bass and keys. I’ve been impressed.

reverb.com

Fender KXR100 1990s - Black | Reverb

Great for the singing songwriting keyboard player to plug in multiple keyboards, and a mic, all at the same time with separate volume controls.Full range with horn, it also works great for acoustic guitar, steel string or classical. Great results with my cello too, or even upright bass.Ships rap...
reverb.com reverb.com
 
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