dumb phonograph question
 

i bought this old silvertone phonograph at a garage sale for $2, the guy said it works, took it home and needless to say it doesnt- LOL, it has a 25l6 tube in it, anyway-it has a loud hum in the speaker, but when i play a record it slides across it, i touched where the needle is supposed to be and get nothing, so i figured i wont find a needle for it and decided to try making an amp,2 lines from the needle i see, ground and signal- when i contact them (signal) with a screwdriver or guitar pickup, i still get nothing, the hum is from the turntable motor, when i disconnect that, the hum stops- so how can i check this thing to make a hobby amp out of it? im not sure if im checking it right, TIA, john

I did this when I was about 9 years old. I removed the cartridge for lack of a better word. I put a stiff wire bent into a rectangle into the needle holder and taped it to the sound board of my drug store guitar. It did amplify the sound. Fortunately it never left my bedroom. The record player was line operated and did not have a power transformer. I could have electrocuted myself if I touched ground. Be careful.

Honestly, you may need a professional amp tech. The 25L6 and 50L6 tubes were used in the All American Five type electronic gear, and they did not use isolation transformers. That means the chassis is potentially connected directly to mains voltage. Even the later ones can pack a nasty jolt if the grounding capacitor fails, they were just trying to limit the shock to a "safe" level.

Let me say that again: these amps are potentially lethal.

If you mod it to plug in a guitar, you've now created a connection from the potentially live chassis to the guitar strings, and through you to ground if you touch something properly grounded. Those need an isolation transformer to be safe, and a proper 3 prong cord.

This ^^^^^^^^^

A phonograph amplifier has special equalization for use with records, RIAA equalization. It will not sound good at all with a guitar unless this circuitry is removed. This requires knowledge of electronic theory. It's probably not worth taking this amp to a technician because it won't be that good when it's done. It is easy to determine if this amp has a power transformer. If it is a mono amp and has 2 transformers, one is the output transformer and one is the power transformer. An amp with a power transformer is safe to use as a guitar amp.

The way we checked our equipment on-the-job back in the early/mid-60's, before 3-prong/polarized plugs:

• Plug in amp
• Plug guitar into amp
• Turn amp on and allow tubes to warm up
• Turn up volume
• If you hear guitar, you're OK
• If you hear harps, it needs to be grounded... :eek:

Bottom line: you're out all of $2 - buy yourself a low-watt tube amp, get the phono repaired when you have the time/money, and use each for its intended purpose...

ok, thx all, sounds like something i wont get into my very limited experience, ill take it to a friend of mine that works on and guitars and stuff, and see if if he get the phono working or make an amp out of here

Though don't give up the dream...some old tube phono's are great git amps. Look for the ones that also have a mic jack/circuit. The kind that they used in PE class to call square dances. Left is a pp6v6 deluxish, center se el84 (blues jr killer) and right is a se6L6 princeton like on steroids...two came with spkrs in the lids.

https://lh3.googleusercontent.com/kC...IFkw=w367-h275

Quick rule of thumb is that if the amp has weird tubes that start with numbers >12, it's usually one of the transformerless models.

A little more background info:

Those originally tied the neutral wire to the chassis to ground it, and ran the hot wire to power tubes and other parts. This means that if it's plugged in backwards, the chassis is directly connected to a live wire and is carrying full 120V direct from the wall, limited only by the circuit breaker. Generally they were safe as radios since anywhere you could easily touch was insulated (bakelite knobs, wood cabinets, etc).

What Steve DeRosa may be referring to is the polarity check on old amps that did use transformers and two prong cords. These did not directly tie neutral to chassis, they referenced it through a capacitor, popularly known as a "death cap", to keep noise down (AC ground only, no DC). Plug those in backwards, they hum a little and might even tingle a little bit when touching the strings, but won't knock you flat out unless the capacitor has shorted. They're still not safe, though. If something inside the amp shorts to the chassis, there's no path to ground other than through the guitarist and you can end up like Keith Relf of the Yardbirds.

However, you can get into amp-building with very limited experience. Some classic guitar amps like the 5F1 Champ or 5E3 Deluxe are very easy to build and can be bought in kit form with instructions.

Actually, you probably could find a replacement needle if the rest of the arm is intact. Needle Doctor would be a good starting place, probably run $20 or so for one of the old Silvertones.
Brad

im no electronic tech. and thanks to friendly forums like this you learn something new everyday, but the mention of new needles got me to thinking, i searched ebay for a needle on my 15 year old sony turntable, i thought was broken and it sat for 15 years, i gave that a shot because it was only $8- i put it on and its sounds great!!, with that out the way being able to play 33's now, ill take the old silvertone next week to our 'senior' acoustic session, ill see the guy up there that works with older stuff and see about making a very small tube amp out it now, if i ever get this done ill post an image of it, if i dont, well you know it ended up in the garbage- LOL