Hello all, I have had in storage for 3 years a McIntosh MC-240, Marantz 8B, Conrad Johnson PV-5, and Scott 350B. I need to wake them up....at last I can set it up again. I once had the system brought up by an engineer who knew tube gear but he is no longer available. I've had the gear 20 years, was in use for many years. All original caps etc. I have a Variac.
I remember the engineer told me it's not just a matter of bringing the voltage up slowly on a Variac, but there is more involved, and that I could blow a tranny if not done right. No tube techs in my small town.
Can any serious technical types give me some advice?
Thanks much,
Jim
I remember the engineer told me it's not just a matter of bringing the voltage up slowly on a Variac, but there is more involved, and that I could blow a tranny if not done right. No tube techs in my small town.
Can any serious technical types give me some advice?
Thanks much,
Jim
Hi Jim,
I think 3 years is hardly any problem but since you have a variac and (it seems) the patience, why not bring it up gently... After all it's all good and valuable kit.
Not sure what your tube-tech meant by there being more to it than a gradual ramp-up. Will be interested what others think...
I think 3 years is hardly any problem but since you have a variac and (it seems) the patience, why not bring it up gently... After all it's all good and valuable kit.
Not sure what your tube-tech meant by there being more to it than a gradual ramp-up. Will be interested what others think...
I would check the power amp tube bias during the variac power up. This way you can catch a run away bias circut before you blow a tranny, fuse, resister. Aside from caps that could change values, sometimes oxidation can cause an open circut on power tube pins and disrupt the proper bias function.
Brought up a HK Elite 300a that had been stored for 30 years. I had no variac, so I let it have it. Bad noises until the caps started working again. Powers up fine now, but I still plan on re-capping it unless I get a good offer on it. (Original tubes!). I did re-seat the tubes; that is good advice.
My first decent set was a pair of mc 30s that had been in my father in law's attic for about 30 years. I knew no better and simply hooked them into my system, plugged them in and fired them up. They worked flawlessly from the time I turned them on until about 8 years later when I found out how much they were worth and sold them....
If I were you I would ramp up with the variac and not worry too much.
If I were you I would ramp up with the variac and not worry too much.
Would it be a good idea to initially power up with the tubes (at least the power tubes) removed? (Keep the rectifier in place!)
- Say, zero to about 100 volts on the mains, ramped up over 60 seconds or so.
- Let it run for 5 - 10 minutes, check the power supply voltages - the intent of the low line voltage is to prevent overvoltage conditions on the unloaded supplies, but if the supply voltages are more than about 15% low, some troubleshooting may be in order.
- Then ramp back down to zero volts mains input, and install the tubes.
- Ramp up the mains voltage to full rated value (or even 130V, if your variac has the +5% boost tap) over 30 seconds.
- Do a quick check for excessive cathode current (a visual scan for glowing plates is probably adequate) and correct if necessary.
- Let the gear run for an hour or two - applying a little program material is probably in order.
- Then make whatever factory adjustments are available (cathode idle current, balance, screen voltage, B+, etc).
- Enjoy it for a few days (warm your hands, keep the tea hot, maybe even listen to some music!) and re-touch the adjustments.
Some of that gear may have been 40 years old before it went to storage. Even very high-quality gear of that vintage should be given some circumspect TLC.
Dale
Thanks everyone. Speakerfritz, what would be good and bad bias voltage values (I presume we're talking voltage)? I suppose I can find the points to tap into with some googling...
Jim
Anything that is over 30 years old and has not been operated in 90 days should be approached with caution. If the unit has been restored with new caps, then different story.
I'm a little concerned that no one has touched on the fact (except speakerfritz) that all of these pieces have their original and in some cases as much as 50 yr old electrolytic caps. Reforming is well and good, but after 20 yrs of known continuous use and then 3 yrs sitting and deteriorating further these capacitors probably do not have a whole lot of life left. (Just their age alone makes them suspect.)
I would be seriously thinking about replacement at this point. Both McIntosh and Marantz used high quality electrolytics in their designs, but after 30yrs or so they would be tired, and are now well beyond that.
I would be seriously thinking about replacement at this point. Both McIntosh and Marantz used high quality electrolytics in their designs, but after 30yrs or so they would be tired, and are now well beyond that.
Whether explicitly stated or not, deteriorated electrolytic capacitors are a major reason for the whole "bring up the voltage slowly" technique.
Are you suggesting that electrolytics (at least, the power supply filter capacitors) should be replaced before even attempting to power up the gear? There is certainly no harm in that approach, and may be the most prudent strategy if "river251" is determined to keep the gear and place it in service at all costs. On the other hand, if he has even moderate success with powering up the gear in its current condition, he will be in a better position to estimate the scope of required repairs. If the necessary work is extensive he may decide to pass the equipment on to somebody else with the talent, time, and treasure needed to do a first-rate restoration.
Dale
Gear that valuable? Absolutely, it's hard to put the smoke back in. It's not a matter of "if", it's "when" the 50 year old caps are going to fail.
A $10 All-American 5 radio, have at it.
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