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20180807_115859 by raindance posted Aug 12, 2018 at 12:31 PM They were used in computers like the Eniac. Saw this in Los Alamos:

I had one of these and mapped out the circuit some years back. It's garbage. The rectifiers arc at startup due to the cap being too large. There's no level matching with tone in or out and the output stage is a white cathode follower (like for a headphone amp) driving a 100K volume pot. There's...

AMC CVT-1030 can be a great used preamp. It has useful tone controls that can be defeated. However they were cheaply made and typically need repair. The PCB is thin and cheap and almost impossible to repair without lifting pads. Also the switches get dirty (easy fix) and the volume pot is a...

Gentle reminder ...

Please let me know if you get a chance to take a look.

I don't know if they used the right foam. Johnny_Law - thanks for the kind offer.

I wonder if any Snell E/III owner would be so kind as to let me know how the acoustic fill is installed in the cabinets from the factory? Mine had surrounds replaced by a previous owner and it doesn't look like the stuffing was re-installed correctly, as the foam, which is quite dense...

Guys, there is NO WAY a volume pot will cause distortion. The key is two things: 1. Is the ALPS an audio taper (log)? 2. You disconnected circuitry for the loudness circuit that is not meant to be left open circuit. The ALPS pots (I use the blue a lot) are excellent and track well. They are...

I would use Windex or just a damp cloth, avoiding the base/pins if possible. You can write the tube info on top with a sharpie after cleaning unless you're looking for more bling than that.

Your resistor idea will mess with damping factor and make your speaker sound loose in the bass as well as making it inefficient. Just get a unit that is stable into 4 ohms. Not that easy when you're going vintage. This stuff was built to a price point. My suggestion is NAD.

Are you sure it's low bass? I think it may accentuate mid-bass (warmth). But I'm surprised by your comments. Mine was fairly balanced, I just never cared for it much. Like I said, not very tubey. This is what excessive negative feedback does. Also the 12ax7 tubes can't provide any drive...

I had one of these. My advice is not to splurge on fancy NOS tubes. It's a good intro to tubes but not very tubey sounding aside from having rolled off low bass. I believe that it is the typical Jolida SRPP circuit and that it uses a TON of both local and global feedback to reduce the gain and...

It's worth trying. I've also repaired 6AS7 amps and used a higher wattage power resistor.

Chinese amps are designed for 110V 50Hz. The transformer will run hot and output voltages that are too high on American 120V 60Hz. Purchase an APC Line-R and set the switch on the back to output 110V. This should solve a lot of problems.

Two worst designs I ever saw: Tube Audio Design TAD-1000: These much loved mono blocks run the gain stage off a regulator tube connected in series so as to drop voltage. What they end up with is a power supply that is endlessly fluctuating. This is a unique and silly use of a gas regulator...

So a 6N2 is very similar to a 12AX7 (just 6V heaters). If you modify the wiring to parallel the heaters on a 12AX7 you may use it instead. I've done this successfully in MingDa amps from China.

You'd get 4 separate capacitors. Leave the can in place for looks and mount them underneath. I must say this sounds like a dangerous undertaking for your skill level. You really need someone to guide you and prevent you getting killed in the process.

Use Google - there are lots of posts about doing this with tube amps. Note the following: 1. Your amp will still have global negative feedback which defeats the object of triode. 2. You also have no way of knowing if it will be stable with or without feedback; you'd need a scope to verify...

Her first album is an awful recording. Her voice clips and is distorted in the left channel on most of the songs. On some songs it clips hard on both channels. The sound engineer must have been sleeping when she sang. If you don't believe me, listen with headphones.

For 12AU7's - the Siemens E82CC. Best I've tried.

Russian Mullard re-issue if you want laid back treble with full-sounding bass and nice mids. JJ ECC83S (not the ghastly ECC803S microphonic garbage) for most other things. Sovtek 12AX7LPS only if your system is too dull (these are bright, bright, bright). I find the Sovtek 12AX7WA general...

Geez. I have done this. TWICE. Guess no one is interested in my opinion. It is CHALLENGING to say the least due to the crappy, crappy circuit board.

Yeah !!! Finally someone who understands the difference between tweaking and basic circuit architecture - I totally agree, these amps could be hugely improved by fixing the design. I think the transformers, etc are basically OK - I have a JD1000BRC and it is quite nice, pretty reliable, but it...

To the OP - do you really want help with this preamp?

What's the plate voltage in the amp? These tubes are similar to 6L6 but have quite a low max plate voltage.