"New" preamp, but I got a problem...

Early B.

GV#27 wrote:

Does the amp work OK with another preamp?

The amp works great with my AV receiver. I've been using it for a few days without a problem. I don't have another preamp to try on it.

RuSsMaN

Try different interconns yet? Just thinking outloud.

You still may have some dirty tube pins/sockets. Get some contact cleaner, and some small pipe cleaners. Oral-B (a dental company) sells little 'flossers' on a stick, that work great for 9-pin sockets with a little contact cleaner. Make sure its COMPLETELY dry before powering up.

Early, send me your addy if you want, I'll send you a clean, NOS JAN 6x4, no charge.

Dennis, the outside tubes are drive, for each channel, as you stated. The 'middle' tube is a phase inverter (putting the unit BACK in phase, as the circuit puts it out.

Cheers,
Russ

Early B.

PM sent. Thanks, Russ!!

I'm going downstairs to try different interconnects right now.

RuSsMaN

Cool, I just pulled a 1986 JAN Sylvania, and a 1960's CBS (GE) for you. I'll CAIG the pins and get them out in the next day or two.

Early B.

I changed out interconnects -- same thing.

I'm gonna give the preamp a thorough cleaning tomorrow and try it again.

Early B.

Found an article via google on replacing caps in audio components. I lifted a couple of sentences:

Capacitors also leak. In theory, a capacitor blocks all DC and passes only AC (including audio). In practice, however, a capacitor will pass some direct current; some types, such as film capacitors, pass almost none, while many electrolytics leak a lot. (Incidentally, most power supply caps leak a great deal when the piece of equipment is first turned on; they stabilize after about 30 minutes, and leak less. This is one of the reasons equipment sounds better after it's been warmed up.) Replacing capacitors with low-leakage units is always a good idea.

This may explain why the manufacturer suggested that I replace caps. What do you guys think?

I'll also try letting the unit warm up for 30 minutes before trying it again.

Ricardo

I would think that the manufacturer in his poor English he might be telling you that that's the fix they found for that unit???

I always thought that "leaking" capacitors meant that they would leak some kind of "juice", like batteries.....

Early B.

Hooked the preamp up again today after cleaning it a little more. I let her warm up for about 30 minutes, then played some music. After about one minute, the Marsh amp shut down again, so the problem persists. I also noticed that even when music wasn't being played, the amp would cut off, then cut back on after about three seconds.

I'm gonna try one more thing before I contact the seller -- put the stock tubes back in and see if it makes a difference.

Systems

In your pics of the unit the larger blue capactors that are attached to the tubes might be the ones connected to the outputs?These appear to be film caps of decent quality.Film caps are very reliable and unlikely to fail.Do you have schematic of the unit that you can post?

The caps that the manufacturer said to replace are in the power supply.If they were faulty(leaky)you would have a problem with hum but the unit should work other wise unless they completely fail then a fuse would likely blow.
Although electrolytic caps can physical leak fluid ,the term leaky is meant electronically as in leakage current in the cap not fluid leakage.

Early B.

GV#27 wrote:

Do you have schematic of the unit that you can post?

The caps that the manufacturer said to replace are in the power supply.If they were faulty(leaky)you would have a problem with hum but the unit should work other wise unless they completely fail then a fuse would likely blow.

I don't have a schematic. I requested one from the manufacturer.

The preamp produced a very loud hum when I first plugged it in. I had to attach a cheater plug to keep it from humming.

Systems

Early B. wrote:

I don't have a schematic. I requested one from the manufacturer.

The preamp produced a very loud hum when I first plugged it in. I had to attach a cheater plug to keep it from humming.

I suspect that was a ground loop issue if the hum stopped with the cheater plug.If it were the capacitors the hum would have still been there even with the cheater plug.
Hopefully they send you schematic they are nice to have if you want to repair or do mods.

Early B.

I just received another response from the manufacturer (it contradicts the previous one):

Dear Sir

Other , i have some experience about this problem.

Many time , this problem is from the protection stage of some solid state amplifier. this is not from the preamplifier.
Some solid state amplifier's protection stage has little lose ( not full lose , is little lose ) , it cannot accept higher voltage input .
when, the higher input voltage to go this power amp ,
the protection part of the power amplifier misidentify this is DC voltage or the overload input voltage setting of protection part is change to lower.
so, the power amp going into protection mode .
This amplifier need repair.

Because , Many tubes preamp has higher dynamic range ( higher output volte ).
So, this power amp connect the good dynamic tube preamp has this problem.
This power amp connect to other solid state preamp or direct to CD player has not this problem.

Thank
Chui Chi Wai


I don't know what to believe.

Systems

His reply makes no sense. You control the amount of voltage to the amp with the preamps volume control,so listening at normal levels should be no problem with an amp the caliber of the Marsh.

You might want to email Marsh and see if they have any suggestions as to what kinds of things will activate the protection circuit.

Systems

Did you get this baby to work yet?

Early B.

Nope.

I thinking it's one of two problems:

1. The pre simply doesn't mate well with my amp; or

2. The pre needs new caps to work with my amp. Unfortunately, I don't have a spare amp to determine if the pre will work with it.

I think the problem is likely to be #1. Nevertheless, the pre doesn't work for my setup, regardless of the reason. I contacted the seller for a refund, so we're trying to work it out.

Even if he doesn't agree to the refund, I'll sell it. But first, I'll very reluctantly take the pre to my friend's house and plug his tube monoblocks to it, then see if everything works. He temporarily dismantled his system (he had to put the Christmas tree in the spot where his system was set up), so he may not want to set up his system again until after the holidays.

Joey_V

Good luck Brad.

Early B.

Took the pre to the shop last week. They replaced the voltage regulator and two diodes. Easy fix. Problem solved.