Silvertone 1472 0n the bench(Platefire)

[rafe]

Shoutout to PF for his 1472 posts from 2016. Nice layouts . I have replaced the electrolytics with 8,16 and 22 500v. the 10/25v. and the .50 ( C15) with a .68. All the voltages are very good..... replaced a few out of spec. resistors tubes are good .....I don't have the 2 68 ohms across the heaters nor are the inputs grounded(yet) It has a hum that follows both volumes, it's dead silent when off It stops when I pull either preamp tube. Tell me about Sangamo caps do they hold up well (1961) I don't want to shotgun, them if not necessary. The owner is a blues harpist and says it has always done this (35+ years) and he was ok with it ...I'm not.

[rafe]

Silvertone1472.pdf

[Latole]

 68 or 100 ohms or anything close is a must for heaters. No ground reference = hum
Ground power cable too.

Input shorting jacks will kill some noise

[Latole]

Silvertone1472.pdf

[danhei]

Sears must have gotten a very good price on 330K resistors.

[rafe]

I know it shows the 68 ohms on the schematic, this amp never had them ...I believe it came from the factory this way.  The 1482 is almost identical and it does not have those resistors across the heaters SANGAMO caps? I'll put in those caps later today....

[Latole]

I know it shows the 68 ohms on the schematic, this amp never had them ...I believe it came from the factory this way.  The 1482 is almost identical and it does not have those resistors across the heaters SANGAMO caps? I'll put in those caps later today....

I see 68 ohms on schematic , 100 ohms or close will do the job

Many of budget amps  (compared to the Fender Marshall, Traynor) I work on, often had assembly errors.

All tubes amps : Heater transformer secondary winding must have a ground
1- Center tap
or
2 - artificial ground with two resistor

[Platefire]

Hay rafe

Want to clarify. You said that the hum stops when you pull either pre-amp tube. I didn't see where you said you tried and known good 12AX7 in either position to see if that corrected the hum??

I have had problems with the 2.2K cathode resistors causing hisss but you said hum. Might be worth a try to change those resistors.
 
Those inputs are grounded directly to the chassis through the input nut mechanical connection to chassis, no wired solder connection! You might try removing those input nuts and cleaning the mechanical connections. Also clean those tube sockets with some good contact cleaner.

Hope you find it! Plate

[Latole]

Hay rafe


Those inputs are grounded directly to the chassis through the input nut mechanical connection to chassis, no wired solder connection! You might try removing those input nuts and cleaning the mechanical connections. Also clean those tube sockets with some good contact cleaner.

Hope you find it! Plate

The tip of the input Jacks are a open circuit and act like antenna when nothing connected . Amp need shorting input jacks.
If Raf can plug 3 guitars and hum stop , it is the jack the issue.

[Platefire]

Well Yeah, the new shorted jacks would be the best. I kinda got the idea he was trying to keep it stock as possible???
Here is a 1482 schematic that came in the manual with each amp. The heaters had a grounded center tap

[rafe]

 I put these in and the hum is negligible at full volume .....Passed the test ....If He wants to change the inputs, I'll be glad to oblige, but I would be OK with it !

[rafe]

 "I'll put in those caps later today....", I meant resistors

[rafe]

Thanks Platefire, The grounds on inputs are good .....i was referring to changing them over to shorting jacks, but I don't see the necessity now. Amp sounds great now I had done all the normal service before I posted on here.  Pots, jacks, tube sockets all cleaned, sockets tightened, 3 wire cord 5 caps replaced (4 electrolytics and one waxed) Tested all the resistors and replaced any too far out of spec (one was open) It looked like someone could have been in there before, but it could have come from factory like that too. It was decent work but some connections were twisted together and soldered, I have never worked on a (Danelectro???) before so don't know the quality on there sears products.

[Platefire]

Glad it's sounding right to you now . As cheap as the 1472's and 1482's were made, they have lasted years and years and years and as of now, still going!

[Latole]

Well Yeah, the new shorted jacks would be the best. I kinda got the idea he was trying to keep it stock as possible???
Here is a 1482 schematic that came in the manual with each amp. The heaters had a grounded center tap

Keeping it original is always my first choice.
Unless the amplifier isn't working properly and assembly faults are apparent.

Which is the case here.

[Latole]

Well Yeah, the new shorted jacks would be the best. I kinda got the idea he was trying to keep it stock as possible???
Here is a 1482 schematic that came in the manual with each amp. The heaters had a grounded center tap

Reply #3

[Latole]

I put these in and the hum is negligible at full volume .....Passed the test ....If He wants to change the inputs, I'll be glad to oblige, but I would be OK with it !

Heater grounded resistors ?

[rafe]

I put these in and the hum is negligible at full volume .....Passed the test ....If He wants to change the inputs, I'll be glad to oblige, but I would be OK with it !

Heater grounded resistors ?

Latole, Go back 7 posts I highlighted the schematic.....They were never put in at the factory, the schematic may be a later revision on the 1472

[Platefire]

I have layout drawings(2) of the 1472 someone created if anyone is interested

[Latole]

I put these in and the hum is negligible at full volume .....Passed the test ....If He wants to change the inputs, I'll be glad to oblige, but I would be OK with it !

Heater grounded resistors ?

Latole, Go back 7 posts I highlighted the schematic.....They were never put in at the factory, the schematic may be a later revision on the 1472

I know, I just said it  is a must if you want a quiet amp.
Read my answer #7

[rafe]

I have layout drawings(2) of the 1472 someone created if anyone is interested

I found that layout , He did a great job on it.....I wrapped it (1472) up this afternoon and played through it for an hour or so. It is a great sounding little amp. I used the instrument channel with my old A S tele and it sounded pretty good (i know) the mic has more gain (maybe tomor r r r o) It's been a harp amp for35 years ....can't wait to get it back to him

[Platefire]

I always thought a tele sounded great through a 1472/1482 because they tend to be dark amps and that kind of takes the super bright hard edge off a tele and mellows it out in a good way. I know your harp playing customer will appreciate a quieter amp.

Well I think there is one mistake on that layout I know of, R38, one of the two artificial heater grounds/taps needs to be hooked up to the other side of the pilot light as picture below. They are both hooked to the same terminal incorrectly on the layout.

[Latole]

I always thought a tele sounded great through a 1472/1482 because they tend to be dark amps and that kind of takes the super bright hard edge off a tele and mellows it out in a good way. I know your harp playing customer will appreciate a quieter amp.

Well I think there is one mistake on that layout I know of, R38, one of the two artificial heater grounds/taps needs to be hooked up to the other side of the pilot light as picture below. They are both hooked to the same terminal incorrectly on the layout.

Didn't I already mention errors in these “low/mid-range” amps?

[Platefire]

Latole
There never was any layout drawings on either the 1472 and 1482 from Sears. Sears only ever provided schematics. This layout was created by an individual I ran across on the net that was working on his 1472 and just decided to create one. This layout might have more errors, I haven't checked it close, just ran across the R38 hookup mistake as we were discussing heater grounds

[rafe]

I did a quick overview of the layout, after I had done the work off the schematic ....it never had the 68 ohms to ground, that's not where I Put them. Owner is very happy with the amp and how quiet it is .....I think it was an early amp and they just didn't call for them or the builder missed them, but that's just a guess......Perhaps the guy that drew the layout was actually looking at them wired that way?? stranger things have happened on a Monday 

[Platefire]

I've got two 1482's. One is completely stock down to the two conductor cord and original filter cap can. The other I modded to my hearts content and more or less modernized with stand-by switch, three conductor cord, new filter caps, coupling caps and resistors, switchable pre-amp cathode bypass caps, switchable negative feedback, new switch-jack input jacks hooked up fender style, new 3/8" plywood baffle with 12" Cannabis Rex speaker hooked to the 8Ohm OT tap, re-designed open back back plate and a Princeton 5A2A tone stack on the mic channel.

Even with all that you can set them side by side and both have a very low operation noise that is very tolerable. So even though these old amps were designed down to the very lowest price point for a low budget they still have brought a lot of joy to a lot of folks:>)

[rafe]

I have to admit that for what would have been a very cheap amp most of the components have held up very well ....The Sangamanolian caps are fine all but a couple of resistors are fine Power tubes are original and tested very good....someone replaced the two 12ax7's with 7025's(USA) but the owner has the originals not sure about the other 2 tubes but think they are replacements ....I replaced the lamp cord 2 prong, but it was still good. all 4 sides of the cabinets had the tolex rolled off ....I used super glue to harden the Paper Mache (lol) and unrolled the tolex and it met up tight and looks 99%+ at 5 feet away All in all Kudos to the crew that made these with the materials they were given. Well Done.......

[Platefire]

Amen!!!