Okay, here's the next update on the G40C resurrection project.
Before I get into the amp details I want to pass on some info I found on DeoxIT and hopefully save someone else the time & effort of dumpster diving on Google for it. In short, there's conflicting info on which DeoxIT products to use on potentiometers, even from Caig. Here's the two "official" options I found.
Now, on to everything I've done since the last update...
So, after all the cleaning and repairs I got everything back together, fired it up, and everything worked great! The channel switching works fine now, the volume will stay where you leave it, and none of the knobs have any static. I was surprised the texture of the business card along with the DeoxIT was enough to clean the contacts on the jacks. I would have thought a more aggressive mechanical polishing would be necessary to get good continuity.
With everything working again I sleeved the speaker wires (yeah, completely unnecessary, but I wanted to keep them from getting snagged so easily, and to me it looks better than just twisting them together) and also cleaned up the cabinet carpet piling (with a Norelco beard trimmer - I stumbled onto that trick at TalkBass.com).
Here's the resurrected G40C...
It still sounds great and the way I remember it after all these years. 🙂
There's still some cosmetic items I'd like to take care of: I need another red knob or at least the red plastic insert (somehow the red insert in the original got knocked out).
The metal ends of the handle on top are a little rough, and some of the cabinet screws are either rusted or corroded. Nothing that affects performance, but I've come this far. So, if anyone knows where I can find an 80's Crate red knob...
Many, many thanks for all of the comments and advice shared here in this thread. I'm hoping that by documenting what I've done with mine the next person who starts troubleshooting their vintage Crate will have this info to guide them and expedite their restoration.
The warranty may have expired 30 year ago, but the amp hasn't. 🙂
Before I get into the amp details I want to pass on some info I found on DeoxIT and hopefully save someone else the time & effort of dumpster diving on Google for it. In short, there's conflicting info on which DeoxIT products to use on potentiometers, even from Caig. Here's the two "official" options I found.
- Option 1: On unsealed rotary pots use either DeoxIT D-Series 100% spray (D100S-2) or 100% liquid (Part No. D100L) depending on how they’re mounted. (Source, Section H)
- Option 2:
- For most volume and other rotary pots use DeoxIT D5S-6, DN5S-6N (also 2N), or D100S-2.
- If the volume pot is relatively clean and just needs deoxidizing and lubrication then use D100S-2.
- If it was subjected to lots of dust, dirt, oxidation or has just been sitting around for a long time use either D5S-6 or DN5S-6N (also 2N). DN5S will evaporate faster and drip less.
- For slide switches/pots and/or conductive plastics use DeoxIT Fader F5S-H6 and then DeoxIT FaderGrease if you want additional tactile feel. (Source)
- For most volume and other rotary pots use DeoxIT D5S-6, DN5S-6N (also 2N), or D100S-2.
Now, on to everything I've done since the last update...
- Cleaned all of the Cliff jacks.
- To clean the TRS contacts I put a drop of D100L on a 1/4" TRS plug in line with where the jack contacts would ride, inserted/removed the plug 10-20 times, then cleaned the inside of the jack with a Q-tip.
- To clean the side contacts I cut an old business card into ~3/16" strips (thin enough to fit between the contact dividers), put a small drop of D100L on the end of the strip, inserted the 1/4" TRS plug into the jack to open the side contacts, inserted the strip with D100L in between the contacts, removed the TRS plug from the jack allowing the contacts to close on the strip, worked the strip back & forth over the contacts, then removed the strip. (I found it helpful to hold the strips with a hemostat while working them back & forth.)
- Cleaned all of the pots. I turned the chassis upside down with the knobs facing away from me, raised it up about 10" off the surface of the workbench, and rested each end on boxes. This gave me room to get underneath to access the back of the pots with their openings facing up. I bent the end of the red spray tube (with a little help from some heat) so that it would spray down into the upside down pots. With the spray tube resting against the wafer and facing down I gave each pot one short shot of DN5S-2N and then spun the knob back and forth several times. I did notice the pots turned a whole lot easier - like too easy - for several turns after I sprayed them but then eventually went back closer to "normal" after a minute or so.
- Replaced all the rubber grommets on the reverb tank. The old grommets had decomposed and melted, so I figured I'd replace them since I already had everything apart. (Many thanks to Jim Winter at Winter Sound Music for the replacements.) I didn't know whether to install the thick side up or down; to me it made sense to place the thicker part where the load would be (i.e., between the screw washer and the pan flange pushing down on it) to cushion it. Someone let me know if I installed them upside down.
So, after all the cleaning and repairs I got everything back together, fired it up, and everything worked great! The channel switching works fine now, the volume will stay where you leave it, and none of the knobs have any static. I was surprised the texture of the business card along with the DeoxIT was enough to clean the contacts on the jacks. I would have thought a more aggressive mechanical polishing would be necessary to get good continuity.
With everything working again I sleeved the speaker wires (yeah, completely unnecessary, but I wanted to keep them from getting snagged so easily, and to me it looks better than just twisting them together) and also cleaned up the cabinet carpet piling (with a Norelco beard trimmer - I stumbled onto that trick at TalkBass.com).
Here's the resurrected G40C...
It still sounds great and the way I remember it after all these years. 🙂
There's still some cosmetic items I'd like to take care of: I need another red knob or at least the red plastic insert (somehow the red insert in the original got knocked out).
The metal ends of the handle on top are a little rough, and some of the cabinet screws are either rusted or corroded. Nothing that affects performance, but I've come this far. So, if anyone knows where I can find an 80's Crate red knob...
Many, many thanks for all of the comments and advice shared here in this thread. I'm hoping that by documenting what I've done with mine the next person who starts troubleshooting their vintage Crate will have this info to guide them and expedite their restoration.
The warranty may have expired 30 year ago, but the amp hasn't. 🙂
Greetings
Seen a notice in email that you had posted progress.
On the Caig sprays, I have 2 types in my home shop.
D Series, 5 oz, D5 - I use on metal contacts of all sorts.
And F series, 5 oz, Fader F5 - for rotary and slider pots - cleaning and lubing the resistive surface and the moving contact and there is necessary conduction to account for where the moving contact is electrically connected for instance to the usually center pin on a typical rotary pot....
Sounds good on the jacks what you did.
Yes, pots can have a bit of a thicker lube on the knob shaft itself that gives a bit of a feel of smoothness and not a loose "freely" rotation. Using spray cleaner can affect that. Flooding the inside of the pot can reduce the viscosity of that shaft lubricant...
I see in the photo the reverb tank grommets had deteriorated significantly. Considering the age, not unusual. I think you are fine.
Very happy to hear the amp is acting more as it should with the maintenance performed. Much of what you did is routine necessities.
On that knob cap - I had stocked a few over the years, they did sometimes come off.
Well, I looked in my parts drawer for Crate and discovered one Crate knob cap left. It is a black cap for the end of the knob. Sorry no red. If you are in the US - I would be willing to mail it to you in an envelope for no charge. Doubt I will be using it anymore...
We could private message any details on that - I am in NE Ohio
Or I could just post my email address - have not done PM on this site that I recall.
Not sure if the thickness affects postage. Probably does. No biggie. Guess I could check with the local post office.
Glad you are having success
Carry on
Deric
Seen a notice in email that you had posted progress.
On the Caig sprays, I have 2 types in my home shop.
D Series, 5 oz, D5 - I use on metal contacts of all sorts.
And F series, 5 oz, Fader F5 - for rotary and slider pots - cleaning and lubing the resistive surface and the moving contact and there is necessary conduction to account for where the moving contact is electrically connected for instance to the usually center pin on a typical rotary pot....
Sounds good on the jacks what you did.
Yes, pots can have a bit of a thicker lube on the knob shaft itself that gives a bit of a feel of smoothness and not a loose "freely" rotation. Using spray cleaner can affect that. Flooding the inside of the pot can reduce the viscosity of that shaft lubricant...
I see in the photo the reverb tank grommets had deteriorated significantly. Considering the age, not unusual. I think you are fine.
Very happy to hear the amp is acting more as it should with the maintenance performed. Much of what you did is routine necessities.
On that knob cap - I had stocked a few over the years, they did sometimes come off.
Well, I looked in my parts drawer for Crate and discovered one Crate knob cap left. It is a black cap for the end of the knob. Sorry no red. If you are in the US - I would be willing to mail it to you in an envelope for no charge. Doubt I will be using it anymore...
We could private message any details on that - I am in NE Ohio
Or I could just post my email address - have not done PM on this site that I recall.
Not sure if the thickness affects postage. Probably does. No biggie. Guess I could check with the local post office.
Glad you are having success
Carry on
Deric
KILLER speakers for a small amp.
Of course, it never hurts 🙂
I bet they are a great factor in the excellent sound you get.
It is way beyond me why many people despise excellent quality and sound Crate amps.
Of course, it never hurts 🙂
I bet they are a great factor in the excellent sound you get.
It is way beyond me why many people despise excellent quality and sound Crate amps.
Deric, please don't post your email address. Not unless you disguise it somehow. Spam bots regularly skim forums like this looking for email addresses
I own a slightly newer version of the G40C with tolex instead of carpet and Crate speakers instead of Celestions. My only issue with it is the slight hiss but I've heard that's normal for that amp. I just got a noise gate pedal to fix the problem. Anyway this thread was a great read and very informative. I am curious though, is there another way to subdue the hiss? I know the Roland JC-120 has the same issue but I've heard it can be fixed by replacing a diode or two. I wondered if there was a similar fix for my Crate?
Mine has a slight hum after the initial pop-hum when its turned on. The "background" hum gets louder and adds a little hiss when you turn up the Level/Volume up past 1/3-ish. Turning on the chorus creates some hiss, either accentuating what's already there or introducing some. I just chalked it up to 35 year old, mid-tier, solid state amp design. I'd be curious to know if there's any mods that could help clean it up some.
Post the schematic of your Crate; perhaps then someone can help. Is it using the dreaded TL072 ICs that were so popular in the 80s? If so, right there is wher you can reduce the noise---by replacing those with OPA1656s.
Link to schematics of the Crate G40C is in the first post (https://loudaudio.netx.net/portals/loud-public/#asset/1660). Not seeing a TL072 in the materials list.
