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I have read the archives about using a variac, and or the light bulb trick. I have access to a variac. I am wondering since this amp uses the 5AR4 rectifier What do I do? I do not have a SS rect. replacement for this tube. Would the light bulb trick be better then the variac?
Help.
-Dave
Follow Ups:
You can use the light bulb 'trick'. I have perform this on & off for 30 years! I just did this on a Fisher SA-100 that was stored since the late 1960s. The variac medthod is better as you have excellent control. The 40 to 60 watt light bulb does add more risk.Before starting this proceedure, make sure the equipment is at room temperature & condensation is not present. A room temperature soak for 24 hours is good if no condensation was present. If condensation was present I would let the equipment soak for 4-5 days at room temperature. Chech the amp for any smoked parts. A slight dull color on the parts is not necessarily a bad part. Black or dark grey is suspicious.
First, if your rectifier in good condition it will conduct at about 2.5 to 3.0 volts filament. It just takes a minute or so. I used a 60 watt light bulb on my Fisher SA-100. I shorted the speaker output terminals with a jumper wire and kept all tubes installed. After something less than a minute you will measure B+ voltage. Start pulling the small preamp tubes one at a time until approximately 150-175 volts is present. Let this amp sit for a few hours at this voltage. Next, remove tubes to get an increase to 200 volts. Take the amp up in approximately 50 volt steps and let sit at that increased voltage for an hour each. Once all tubes are removed, you should have approximately 325 volts. That voltage depends upon your bleeder resistors and other resistive circuitry.
If you are not capable of measuring this high voltage, you will have to perform this in a slower process. Assuming the 60 watt bulb is in series with the 120vac line voltage input. Turn on the amp & let the amp sit for 3-4 hours then pull one tube at a time every 30 minutes starting with the smaller (less tall) preamp tubes after the first 3-4 hour soak. After all tubes are removed, shut off the amp & reinstall all the tubes. Remove 60 watt bulb and power up at full line voltage. If any time during the process the lamp goes and stays bright, you have a short. Then, the amp must go to a technican.
My 2 cents.
.
~~b
Thats the problem. How to apply a small amount of voltage in a controled manner.Rodney
The GZ-34 problem is under 2.5 volts as the rectifier will conduct at a low 2.5 to 3.0 voltage. My post using the 60 watt bulb will apply slightly less than 1/2 normal B+ voltage. However, the light bulb without a variac & solid-state rectifier is not the better system.
...call me careful, anal, whatever, but at $35 a pop I try to be as gentle as possible.Take care,
Rodney
Agreed, 1/2 voltage is increased risk as I stated in other posts. I usually just replace the electrolytic cans before restarting old gear. I find some electrolytic can type capacitors for $3 each at AES Tempe, AZ rated for 350/400 VDC with reasonable capacitance ratings. Other higher voltage can type capacitors are $30 each.
Jimmy,This is what I do. For most apps, this works out fine. Ramp slow and steady over 6-12 hours. After 80 VAC, you can replace the 5Y3GT with the GZ34, if you wish.
item T-SSR01; www.tubesandmore.comI wouldn't use it as a replacement as such, but it should be just the ticket for bringing up old gear w/tube rectifiers s-l-o-w-l-y with a variac, if you're not up to or in the mood to make your own on an old tube base
...Well, you have a decent unit, well worth it to take your time here. As you seem to realize the GZ34 will not pass current until the heaters warm up. This attribute makes it difficult to bring the entire amp up under a variac. There are a couple of ways to go here. I will recomend the one least likely to cause problems. Remove the GZ34 and replace it with a solid state rectifier. This will allow you to bring it up without problems. You can make your own ss rectifier using an old tube base, or can purchase one from a number of sources.There is some debate as to what to do with old electrolytic caps. I have certainly seen 1940's stock that still work fine during daily use. However, the lifetime of caps can be shortenned by operating voltage, storage conditions, ect... So you will want to check the amp for signs of previous failure (burnt resistors, ect...) and make sure the caps have not begun to deposit a white/ light brown substance at their base. Fresh multi-section caps are available at many suppliers if you need to replace them.
When I intend to keep an amp for a while, I tend to replace or bypass ALL the electrolytics on consumer gear where the amp voltage is very near the working max voltage for the cap. Some find this anal, and it certainly not the only way to go. As I implyed I have some pro audio gear from the 1930's and 1940's still running original caps without leakage. I have also replaced caps with 1950-1960's fresh stock without problems. However, I have indeed found similiar stock with leakage problems. The take home here is that your milage may vary so be wary and be safe.
One final note, make sure to have a volt ohm meter on hand, so that you can see the voltage being applied. Also, as you bring the amp up on the variac, you will want to check the current draw after the rectifier. If the caps short, allot of current will be drawn. I would not attempt to bring something up without monitoring it. In the long term, caps are cheap, transformers, well, I have a closet full of other people's experiments gone wrong. Maybe one day I will win the lottery, so I can afford to but a whole closet of custom transformers to make them run.
Good Luck,
Rodney
Thanks for the advice Rodney. I also remember reading in the archives that Steve Oda said that there was a substitute tube for the rect. "5Y something" that I could use.
Do you know where I could buy the SS rect. that fits in the tube socket?
This 299-B also came with a Scott 310-D Tuner, do I need to bring that up on the variac?
The previous owner bought them new in 1962 and died in 1965. They were a friends grandfathers and he said that his grandmom never used the Scott's after he died. The 299-B even has Telefunken 7189 outputs and all original tubes in both. He also gave me all the original lit., owners manuals, schematics, letters he wrote to HH Scott, etc.
I am going to compare them to my Sherwood S-5500II tube amp & S-3000III tuner.
-Dave
You can make your own ss rectifier or buy. It does not matter, which ever you feel comfortable with. These are pretty handy to have around. You could substitute anothe rectifier without the slow start up but with the same basing. But I would go ahead and get a ss rectifier. I personally use them despite having a closet full of tube rectifiers. They are handy.Yes, do bring the tuner up on the variac.
You can find more info on these units from the HH Scott site.
Sounds like a great find.
Rodney
Thanks, Russ! Anything special that I need to do when bringing up the tuner on the variac?
-Dave
Remember, the solid-state rectifier does apply more voltage than the cathode based GZ34. Using a variac, I would limit the input to about 100 volts AC.As for the solid-state replacement, perhaps a series dropping resistor is installed to help that over-voltage condition.
Iam only going to use it to power up the amp with a variac. Sounds good to me as to keep it under 100 volts, then switch back to the Tube rectifier for use.
-Dave
Dave,Please be sure to read the postings here and elsewhere (Angela Instruments, ect...) regarding the reforming of old electrolytic caps. I tend to apply a very small amount of B+ at first, say 1-2 volts (You will need a volt ohm meter). This translates to VERY little AC voltage. I then step up to about 10 volts B+ and hold for a while. I then begin a slow, step wise process to about 1/2 the normal B+. Also remember that the downstrem electrolytics will see less B+ than the first section or two, so you need to take that into account. Again you should measure voltage and make sure these caps see 10 volts or so for some time before increasing voltage. As I understand things, the caps reform best at these relatively low voltages. My own measurements of current support this conclusion.
Also, you will need to take the unit up to full operating voltage slowly on the variac. You need to pay attention here because things may fail as you do this (resistors, tubes). Look for smoking parts, check voltages at all electrolytic caps against the published values, ect... Vigilance is bliss, negligence can kill you. Remember if the tubes start to glow red, bring the voltage back down and turn the unit off. Often bias resistors or settings are off when this happens. Most recomend this process be done with a load connected to the output transformers. Speakers or dummy loads will do.
Now, I hope I scared the sh*t out of you. Relax, be vigalent, and you will be fine.
Good luck,
Rodney
After starting up well over 200 pieces of tube gear, I have never experienced a high voltage capacitor failure to date. For the most part, I eventually replace the B+, bias and all coupling caps if I keep the equipment.Anyone else experienced a failure?
.
I figured I have been lucky.
...10% failure of electro's at first start up.
and 10% more that make it for a while before giving up the ghost.I would guess these numbers includes 20-25 int. amps, 30 or so monoblocs and stereo blocs, a 15-18 tuners, preamps, and 4 recievers.
Like you, if I keep it, it gets fresh caps (with some exceptions where cap is very overrated as in some pro gear).
Take care,
Rodney
the easy and cheap way is to remove the tube retifier and tack solder a pair of diodes to the tube socket. A 1N4007 from Radio shack is fine.
Russ
Yes, the tuner has to be brought up slowly. Use a 15 watt bulb, repeat the 'pulling tubes' process as described in my other post.
You are probably right about the 5AR4.
Twenty-five years ago, when I took posession of my LK-72B, it had been sitting for 15 years. Do the math. It was nearly new, when put in the closet. I did the lightbulb trick; but 1st replaced the 5AR4 with diodes, soldered into a socket.
The amp still works today, (with a 5AR4). Look at the schematic, and fashion a rectifier with 4 diodes.
If it's been off a long time then my primary concern is the leakage of the filter capacitors (large aluminum cans). This could be downright dangerous. I would replace them before I would even consider putting 110 volts to it. Otherwise the metal chassis could be hot with DC. Leakage is dangerous! Especially 450 volts of it! I would use the lite bulb in series with the variac. And I wouldn't turn an amp on without some kind of load on the output, ie a dummy resistor load of approsimate wattage or an old speaker. If it has a volume control I would turn it all the way down. On turn on, if the lite bulb glows consinuously then you've got some other issues because it's drawing too much current. If it has a fuse, the fuse should blow. Good luck! James
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