Hi all,
I recently picked up an early Mesa Blue Angel combo (4×10), with a three-digit serial number. As far as I can tell, this is one of the first production units. The amp is roughly 30 years old and, according to the previous owner’s family, has never been serviced. It spent the last 10+ years in storage after the owner moved into a nursing home.
The amp is in good cosmetic condition (tolex, chassis, etc.), but internally it clearly needs some TLC. Part of the reason I bought it was to have a low-volume “bedroom” amp and also to go through it properly from a reliability standpoint.
Below is what I’m planning so far, and I’d appreciate a sanity check and any advice from those more familiar with this platform.
Tubes: I don’t believe the tubes have ever been replaced. I already have a full new set of TAD power tubes. JJ 5751s for the preamp - I chose 5751s because I’ve seen multiple reports that the stock ECC83/12AX7s can be overly hot in this circuit and are a common source of noise.
Power supply & electrolytics: The main PSU electrolytics appear slightly swollen. Given the age, I’m planning to replace all power supply caps. I’ve selected Kemet PEG124 33µF / 450 V caps, mainly for their temperature rating and long service life. I’m also planning to replace all remaining electrolytics (bias supply, cathode bypass caps, etc.) with new parts. The amp uses several tantalum caps; I’m considering replacing all of them with electrolytics.
Coupling caps- The phase inverter coupling caps are rated at 450 V. Given the age and operating margins, I’m considering replacing them with 630 V parts.
Screen / grid resistors - stock screen and grid resistors are 1 W carbon film (CCF60). I’m considering replacing the screen resistors with higher wattage parts (2 W minimum; 3 W preferred, though PR03s likely won’t fit physically) and lifting them slightly off the PCB, increasing screen resistor values from 470 Ω to 1 kΩ
Rectifiers & diodes - planning to replace the preamp-stage rectifier diodes from 1N4007 to UF5408. Also considering adding safety diodes to the tube rectifier.
Dropping resistors - the 100 Ω dropping resistor feeding the preamp supply is also a 1 W CCF60. I’m considering upgrading this (and possibly all PSU dropping resistors) to higher wattage parts for long-term reliability.
Pots, sockets, and general service - the midrange pot is noisy and intermittently cutting out. I could clean it with DeoxIT, but I’m leaning toward replacing it outright.
I plan to clean or service:
- All tube sockets (preamp and power)
- Remaining pots
- Jacks and switches
Once component work is complete, I’m considering reflowing solder joints to relieve PCB stress.
Questions
1. Are there any known failure points specific to early Blue Angels that I should address while I’m in there?
2. Any concerns with replacing the tantalums with electrolytics in this circuit?
3. houghts on increasing the screen resistor value to 1 kΩ in this amp?
4. Is upgrading PSU resistors to higher wattage generally recommended here, or unnecessary?
5. nything I’ve listed that you’d strongly advise against?
I’m primarily focused on reliability and longevity, not trying to fundamentally change what makes this amp a Blue Angel, although - While reliability is the primary goal, I’d also be open to very light voicing changes if there are known tweaks that help control low-end buildup. As the volume control passes roughly halfway, the amp can generate a fair amount of low-frequency mud. I’m not looking to turn it into a different amp or chase higher gain—just to improve clarity and control while preserving the Blue Angel’s core character.
Thanks in advance for any insight.
Mesa Blue Angel service
Moderators: pompeiisneaks, Colossal
Mesa Blue Angel service
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Re: Mesa Blue Angel service
I've worked on a few of these, I would say "bedroom amp" if you happen to sleep in an army barracks. 
I'd hold off on replacing tubes until you see how it works. I just finished repairing an 88-year old car radio, which all 6 tubes were original Philco from 1936 or 1937. Every single tube was still quite good. I have a big stash of used tubes from folks who insisted on replacing tubes during an amp repair. All those old used tubes from the last 3 decades, are better than the brand new tubes I can buy today.
On the electrolytic caps, the Kemets are fine capacitors. I would probably try to keep the voltage ratings the same, or higher. It is kinda weird how they put 500v caps on the preamp power supply and 450v caps on the power section power supply. Maybe they were counting on the 5AR4 to warm up slowly to keep the peak unloaded voltages down. The solid state diodes are going to instantly rectifier peak voltage as soon as the power is on. The only thing that loads them is the pre-amp tubes, which will take 30 seconds to warm up.
If Mesa could have used the cheaper 450v rated caps everywhere, the would have. Might measure the peak voltage with the tubes out at the cathodes of the 1N4007 and that 100-ohm. You need caps that are a bit higher voltage than whatever that turns out to be.
That 100-ohm is common failure point. May as well just jumper it, or at least replace it with a 2-watt MOX resistor of the same value.
On the reservoir filters off the 5AR4, I might replace the 2x 30uf with a single ~40uf, or 2x 20uf (or 22uf) instead, to get a bit more life out of the 5AR4. A total of 40uf is plenty, and it puts less strain than 60uf on the rectifier tube.
In choosing a replacement electrolytic, you can replace those 30uf with anything from 20uf to 40uf (except for the first reservoir off the 5AR4), of suitable voltage. The preamp stage you could easily go down 16uf and have plenty of filtering. The preamp filter caps are higher voltage, because of the SS rectifiers. With the preamp tubes still cold, you can see a lot of voltage on power up on those caps. I would definitely respect the voltage ratings on all 3.
The cathode bypass caps on the output stage seem a bit oversized to me. You could probably go as low as 20uf and it will still sound great, if not better.
My rule is always test first, fix anything broken second, and only third make changes, a bit at a time.
I always recommend initial bring up on a variac with a current limiter first, see what is and isn't working.
Seems like you've already powered it up and done some initial inspection. I'd clean the pots the pots first, that's easy and safe and probably save a bunch of time and aggravation and a few bucks.
I'd definitely leave 470ohm on the 6V6 screens, they're fine. You can leave the 470's on the EL84 too, or change them for higher if they offend you. I'd probably measure them now, see how it sounds, and perhaps up the wattage a bit.
I'd hold off on replacing tubes until you see how it works. I just finished repairing an 88-year old car radio, which all 6 tubes were original Philco from 1936 or 1937. Every single tube was still quite good. I have a big stash of used tubes from folks who insisted on replacing tubes during an amp repair. All those old used tubes from the last 3 decades, are better than the brand new tubes I can buy today.
On the electrolytic caps, the Kemets are fine capacitors. I would probably try to keep the voltage ratings the same, or higher. It is kinda weird how they put 500v caps on the preamp power supply and 450v caps on the power section power supply. Maybe they were counting on the 5AR4 to warm up slowly to keep the peak unloaded voltages down. The solid state diodes are going to instantly rectifier peak voltage as soon as the power is on. The only thing that loads them is the pre-amp tubes, which will take 30 seconds to warm up.
If Mesa could have used the cheaper 450v rated caps everywhere, the would have. Might measure the peak voltage with the tubes out at the cathodes of the 1N4007 and that 100-ohm. You need caps that are a bit higher voltage than whatever that turns out to be.
That 100-ohm is common failure point. May as well just jumper it, or at least replace it with a 2-watt MOX resistor of the same value.
On the reservoir filters off the 5AR4, I might replace the 2x 30uf with a single ~40uf, or 2x 20uf (or 22uf) instead, to get a bit more life out of the 5AR4. A total of 40uf is plenty, and it puts less strain than 60uf on the rectifier tube.
In choosing a replacement electrolytic, you can replace those 30uf with anything from 20uf to 40uf (except for the first reservoir off the 5AR4), of suitable voltage. The preamp stage you could easily go down 16uf and have plenty of filtering. The preamp filter caps are higher voltage, because of the SS rectifiers. With the preamp tubes still cold, you can see a lot of voltage on power up on those caps. I would definitely respect the voltage ratings on all 3.
The cathode bypass caps on the output stage seem a bit oversized to me. You could probably go as low as 20uf and it will still sound great, if not better.
My rule is always test first, fix anything broken second, and only third make changes, a bit at a time.
I always recommend initial bring up on a variac with a current limiter first, see what is and isn't working.
Seems like you've already powered it up and done some initial inspection. I'd clean the pots the pots first, that's easy and safe and probably save a bunch of time and aggravation and a few bucks.
I'd definitely leave 470ohm on the 6V6 screens, they're fine. You can leave the 470's on the EL84 too, or change them for higher if they offend you. I'd probably measure them now, see how it sounds, and perhaps up the wattage a bit.
Re: Mesa Blue Angel service
Thanks for the reply—I really appreciate you taking the time.nuke wrote: ↑Tue Jan 06, 2026 12:15 am I've worked on a few of these, I would say "bedroom amp" if you happen to sleep in an army barracks.
I'd hold off on replacing tubes until you see how it works. I just finished repairing an 88-year old car radio, which all 6 tubes were original Philco from 1936 or 1937. Every single tube was still quite good. I have a big stash of used tubes from folks who insisted on replacing tubes during an amp repair. All those old used tubes from the last 3 decades, are better than the brand new tubes I can buy today.
On the electrolytic caps, the Kemets are fine capacitors. I would probably try to keep the voltage ratings the same, or higher. It is kinda weird how they put 500v caps on the preamp power supply and 450v caps on the power section power supply. Maybe they were counting on the 5AR4 to warm up slowly to keep the peak unloaded voltages down. The solid state diodes are going to instantly rectifier peak voltage as soon as the power is on. The only thing that loads them is the pre-amp tubes, which will take 30 seconds to warm up.
If Mesa could have used the cheaper 450v rated caps everywhere, the would have. Might measure the peak voltage with the tubes out at the cathodes of the 1N4007 and that 100-ohm. You need caps that are a bit higher voltage than whatever that turns out to be.
That 100-ohm is common failure point. May as well just jumper it, or at least replace it with a 2-watt MOX resistor of the same value.
On the reservoir filters off the 5AR4, I might replace the 2x 30uf with a single ~40uf, or 2x 20uf (or 22uf) instead, to get a bit more life out of the 5AR4. A total of 40uf is plenty, and it puts less strain than 60uf on the rectifier tube.
In choosing a replacement electrolytic, you can replace those 30uf with anything from 20uf to 40uf (except for the first reservoir off the 5AR4), of suitable voltage. The preamp stage you could easily go down 16uf and have plenty of filtering. The preamp filter caps are higher voltage, because of the SS rectifiers. With the preamp tubes still cold, you can see a lot of voltage on power up on those caps. I would definitely respect the voltage ratings on all 3.
The cathode bypass caps on the output stage seem a bit oversized to me. You could probably go as low as 20uf and it will still sound great, if not better.
My rule is always test first, fix anything broken second, and only third make changes, a bit at a time.
I always recommend initial bring up on a variac with a current limiter first, see what is and isn't working.
Seems like you've already powered it up and done some initial inspection. I'd clean the pots the pots first, that's easy and safe and probably save a bunch of time and aggravation and a few bucks.
I'd definitely leave 470ohm on the 6V6 screens, they're fine. You can leave the 470's on the EL84 too, or change them for higher if they offend you. I'd probably measure them now, see how it sounds, and perhaps up the wattage a bit.
In hindsight, I probably should have held off on powering the amp up after such a long period in storage. That said, the amp was tested before I put the money down, and once I got it home I had a hard time resisting the urge to play it a bit. I’ve wanted a Blue Angel for a long time.
You’re absolutely right about the tubes, but I’ve already ordered the set. Worst case, I can always keep them as spares or use them for testing.
Thanks for the input on the PSU caps—that’s very helpful. Your suggestion about reducing the total reservoir capacitance off the 5AR4 is interesting. My original plan was to replace them with stock values, but I’ll definitely take your advice into consideration. For the 500 V positions, I actually picked up some 500 V–rated F&T caps shortly after my previous post. I also have a supply of 20 µF TAD audio caps on hand, so I’m covered parts-wise.
I’ll be upgrading the 100 Ω dropping resistor to a 2 W part for sure.
One question: wouldn’t increasing the screen resistors from 470 Ω to 1 kΩ help reduce low-frequency overload at higher volume levels?