Fender Hot Rod Deville

[DüTerra]

Hey everyone this is my first post.

I've been creeping on these message boards for years now. They've been a great resource for information over the years. I also have Bogen Chb35a that I plan to restore or covert which I will likely need guidance or advice at some point. But that's not why I'm here today....

I'm making this post because a friend left his faulty Hot Rod Deville in my care. Long story short is he brought his HRD to the only local amp tech in our area and the guy said a faulty power tube was to blame. I think his tubes were kinda new or something but for whatever reason was he had his doubts.

So, he left the amp with me and I installed a spare pair of 6l6ge and rebiased the amp. I understand the GT 6l6ge to be Groove Tube's version of 6l6gc. I've read somewhere else that 6l6gc are specfically recommended for these HRD amps because of the higher plate voltages (or something) that other 6l6s aren't quite designed for. If someone knows more about this feel free to chime in.

Anyways, I install the spare pair of 6l6ge and the problem persists. What is this problem? Channel switching, God-awful LOUD popping, and volume loss... Nothing new, right?

ok so fast forward to a few hours ago and I popped it open to take my first look at it. I have my bougsie chopstick and I'm poking around in there like a kid trying to bust a piñata. Jk me and my chopstick are careful.... I start with the power tubes, working left to right touching every tube socket pin on the pcb. No problems. So I move to the PI working left to right again and when I get to pin1, all hell breaks loose: The Green/Yellow/Red channel switch is blinking erratically from Yellow to Red to faint Red which certainly isn't normal.

Alright so I take note: pin1 on PI is NOISEY. The amp calms down and I keep chopin' sticks. By the time I finish working left to right through the other 2 pre-tubes it seems like touching almost anything just sends the amp into a frenzy.

The ¿ribbon wires? that connect the tube pcb to the main pcb seems to cause it to act up especially bad when touched. But then again touching the main pcb anywhere is causing noise and pops. Those notorious 5w 330 ohm resistors seem to send it into a frenzy too.

So to recap pin 1 of the PI seems noisey so does the ribbons and those 330ohm resistors. One of those resistors seem loose maybe but there is no signs of overheating or burning. I also visually checked the filter caps for any corosion from leaks, none was detected.

Ok so I turn everything off, drain the caps & resolder pin1 of the PI. Then I turn the amp back on to check if that fixed the problem... it did not fix the problem. Hell continues to break loose, popping and a light show from the channel switch LED.

I started to take the main pcb out but didn't get very far when I noticed that it was getting late. So I start to put it all back together because it might be a few days before I get back to it. And at this point I am wondering to myself if maybe the spare set of 6l6ge tubes I installed at the beginning were faulty as well as the 6l6gc that it came with.

I happen to have a matched set of 5881wgc lying around that I know are good because I bought them new years ago for my 5150 but never installed them.

So just to double check I install the 5881wgc and rebias the amp. And it works perfect! This suggest that both my pair 6l6ge and the original pair of 6l6gc were faulty, right?... So now I want to triple check. So I go back and retest my pair of 6l6ge and they work. Which is not what I would hope to expect in this case. Those 6l6ge were actually from a set of 4 so I test the other two 6l6ge and they work perfect. Then just to hammer it home I test the orginally 6l6gc and they also work perfect.

At this point it's late and it's clear that I am about to catch hell trying to pinpoint this problem.

I feel like it's going to take a lot of troubleshooting and a lot of advice so grab some popcorn and get ready to laugh hysterically at my novice misery as I chase ghosts through this HRD.

but seriously if you have any advice I'm all ears.

[Enzo]

Just from experience, resolder all 16 pins of the power tube sockets. If the PI socket or the other two for that matter look iffy on the solder, redo them. TIny cracks in the solder happen a lot on this series of amps.

But none of the tube circuits will affect the channel switching. The channel switching uses the +16 and -16 volt rails for the transistors, op amps, and relays. And that leads us to another problem we see a lot. The 16v rails are zener regulated, and the zeners get their voltage through a pair of 5 watt 470 ohm cement resistors. SOme model revisions used 330 ohm, but they run even hotter, and if I have to solder there I put 470s in. R78,79. They are right along the bottom edge of the main board next to the bias control. Gently poke at those, are they loose? and does poking cause any reaction in the channel switching?

I suspect when you install tubes, it flexes the tube sockets and their solder connections, so that is why changing tubes makes it work...for a time. The amp really doesn't care what brand tube you use. The voltages in this amp are not far off from a Fender Twin Reverb, which also uses 6L6s and has for decades. it is not at all sensitive about them. Besides, your 5150 has higher voltages. (on the other hand a 5150 runs its tubes REALLY cold.)

It is entirely possible some connections with the ribbons have gone sour. But flexing or moving them also flexes the board and the 330 ohm guys. REpair them first. I do recommend 470 in their place. Check out their solder, it likely needs repair. For sturdiness, I often clean the coating from the copper traces and extend the resistor lead wire along the traces a little ways and sweat solder along that.

[nevetslab]

The Hot Rod series PCB's aren't real good quality. I've been servicing a rental fleet of them for the past eleven years, and do spend a fair amount of time on the back side of the main PCB, as well as on the TUBE PCB's to repair solder joint fractures, as well as having to patch broken solder pads back onto the broken traces that broke away during repairs or component flexing. Once you've cured all the broken solder joints, these run quite nicely. 5881 tubes work quite well in them. Enzo's advice above ^^^^^ is right on with the 5W dropping resistors feeding the 16V 5W zener diodes. Those solder joints do get cooked from all the heat.

Fender's troubleshooting guide to assist in getting the Channel Switching is a GOD-Send, and very accurate. Don't make any substitutions on the channel switching IC....it does need to be that NJM 4560 higher current dual op amp. BiFet op amps will not work there. I've been using a lower gain tube (12AY7) at V2 in these amps, along with inserting 600 ohm resistors in series with the two cathode bypass caps (C8 & C9) to drop the gain down when switching between Drive and More Drive, as the stock gain just rips your ears off with it's 16dB gain increase. 7dB increase is plenty, we've found in our rental fleet, and our clients like that a lot more.

As Enzo stated, the ribbons between the two PCB's is right on.

[glebert]

Has Fender addressed any of these issues in newer models of the HR amps? I've only worked on ones from the first few years, but it seems like they persisted for quite a while.

[DüTerra]

"Just from experience, resolder all 16 pins of the power tube sockets. If the PI socket or the other two for that matter look iffy on the solder, redo them. TIny cracks in the solder happen a lot on this series of amps."

Yup. I found cracks on pin 8 or 9 of the PI and another in one of the 6L6.

"a pair of 5 watt 470 ohm cement resistors. SOme model revisions used 330 ohm"

Another yup. This amp had 330 ohm resistors. I left them in but one of the leads had broken loose and I think this resistor was 90% of the problem.

"The Hot Rod series PCB's aren't real good quality. I've been servicing a rental fleet of them for the past eleven years, and do spend a fair amount of time on the back side of the main PCB, as well as on the TUBE PCB's to repair solder joint fractures, as well as having to patch broken solder pads back onto the broken traces that broke away during repairs or component flexing."

I found another ~10 or so solder joints that looked like potential weak points. A few were cracked, a few were really corroded and the rest were just dull, sloppy or beaded up as is it weren't heated properly.

Thanks for all the help y'all. I actually got it up and running. I played it for a few hours at home with zero noise. Gave it back to my friend where it used for a few more hours at higher volumes. So far no problems. Y'alls advice was on point. Thank you again for your help.

Since my original post I have even been able to troubleshoot and fix my Ampeg VL-502.

Now I have a Bogen chb 100 and a Bogen chb 35a on the bench! I'm going to make a new post about that project tonight. If you have any advice to offer on those amps please chime in.

Y'all I think I have the itis... Today I went to a local print shop and got the schematics for both Bogen amps, my Blackstar, my Kustom and 2 Peavey amps printed out on paper. (I dislike using screens to view blueprints).

[Enzo]

Hi, welcome

I have a huge paper schematic collection, I mean several shelve units fill of three-ring binders. I liked them especially doing a lot of Peavey work, and their drawings were 11x17

But over time, my computer display being right on my bench, I found myself quick calling up a drawing on screen and not bothering to fish out the paper. One thing I like is the ability to grab a part of the drawing and blow it up to see easier.

To each his own, of course, but you might make an effort to give it a good shot.

I have a hard and fast rule, NEVER write on the schematics, unless it is some useful information in general. Nothing worse than pulling out a drawing and find parts circled with BAD written by them, or voltage readings all over from some unit. But it can be useful while working to do so. I can print a screen grab from my screen, and scribble on THAT. No harm to the original.

[DüTerra]

Thanks for being hospitable Enzo.

Man. The Peavey schematics look like rocket science compared to Bogen's. I think the 5150 took up 3 pages! My Delta Blues schematics was 2 or 3 pages as well. That's 8.5x11 though. Schematics for my Kustom did print out on 11x17. I think I'll go back in the next week to print them all out on 11x17. I laughed when I read your comment about NOT scribbling on the schematics, guess what I've already done?... smh...I think I'll get two copies printed out so that I can have a "master" copy and a copy for notes and to keep a record of modifications. I'm not totally against screens I just don't have any large enough that are free to move to my hobby room. Also, from ironwork and fab shops I'm used to the paper format. I do believe you have good reasons though so I'll probably take your advice whenever I can get an extra monitor into my work space.

[Enzo]

Well it depends on your shop too. MY bench was in my pro audio service shop, I used my computer all the time at the bench. If your computer is elsewhere in your house and you are just an occasional techie, I can see a smart phone as a poor choice for schematics. Although I am sure some folks think they are fine. 5150 is not a good first schematic to read. I am used to it, but compare the 5150-2 schematic. Circuit is extremely similar, but is all on one page, not in pieces.

Delta BLues - same circuit as Classic 30 - is all on one page, the other two pages are the layout drawing and a parts list. I blew mine up to 11x17 at Kinkos.

[DüTerra]

Man wish I had a whole shop or even a garage. Sounds like more fun than I could handle though. Probably best I stay a bedroom hobbyist for now until I am more knowledgeable and have a full set of tools (variac, oscilloscope, etc). The only reason I printed out the Peavey schematics was because I already own those amps. I just wanted to have them on hand. I need to dig up schematics for an Ampeg VL-502 and an Egnater Rebel 30 mk1 and I'll have all my amp's schematics on file.

[g1]

. I need to dig up schematics for an Ampeg VL-502

Unfortunately the quality is not great (edit: see Enzo's post #12 below for more schematics, VL1002 is basically same)
https://ampeg.com/support/files/Sche...L-502,%201002/

[DüTerra]

Thanks g1. Have you downloaded those? I feel like there are pages missing.

[Enzo]

http://schematicheaven.net/ampeg.html

[g1]

Thanks g1. Have you downloaded those? I feel like there are pages missing.

Yes you are right. See the VL1002 schematics in the link Enzo posted above. All the same except the 1002 is the 100watt version.

[DüTerra]

Y'all da bess. I can't wait to get these printed out as well. Many thanks.