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Messages - bry melvin

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136
Personally I would try to go a little higher on the VA rating and check to see if transistor and cap voltages were not exceeded but...

using your criteria the closest I see in Digikey is the Hammond 166J36 @36VA single primary 36 V single secondary center tapped

unless I'm missing something that should work.

I didn't check Physical size and fit though

There are other ballpark ones LISTED but not stocked.

137
You can look at what the output transistors are an make a guess. Just as a WAG the total power consumption of that amp is probably < 50 watts. Mouser has Hammond transformers of 54VA that would probably work. Solder terminal ones though. The have others listed...but that's in stock. To get one with leads you would probably need to buy an 80VA hammond which is most likely overkill AND would probably not fit in your amp.

I THINK your "TBA" transformer was made in china although I can't find any more.

If you don't want to wag it you could take it to a tech who could put it on a step/up transformer and test it and make a recommendation.

personally I'd put about a 50 or 60 VA transformer in it or even a little larger if it fit and then make sure the voltage at the power transistors wasn't too high and call it done.


138
18 v X 2 is not always the same as 18 0 18. There could be 18 V 0  18V 0  wires with separate windings. However your picture shows 2 aqua secondary wires and a black. This leads me to believe that you have a Center tappped Transformer.  In the US here that would usually show in a parts catalog as 36VCT

As far as current needs. that is somewhat of an estimate without specs of your amp and transformer. Somewhere on your amp should be a plate saying watts.   Volts X amps = watts so without data you would need to take that formula and figure how many amps your amplifier is expected to draw and buy a transformer accordingly.

139
The Newcomer's Forum / Re: Sears 450G amp
« on: May 07, 2010, 09:48:08 PM »
Solved :
 Replaced Tip31/32 pair of 2n4403s made bigger heat sink on the latter and replaced cooked 1/2 watt resistors with 1 watt ones.

Never did find a schematic though

140
Let me try this again.  I think you need a transformer described as 18-0-18  or 36v CT. for 110 volt primary.

I can' t find a schematic or  cross reference on your current transformer.

Try looking at Hammond In the low voltage section. I think they have one and two amp transformers in this range I'm more familiar with the high voltage ones.

Bear in mind physical size is going to be different.

Antek has 18 -0 -18 Volt transformers too... but torroidal and you would probably need to add a current/onrush  limiter

141
last post might be misleading with the + - as it's still AC at this point.  I think what you have is 18 volts from each blue wire to the black which I believe is the center tap

142
looking at your photo:

The cable comes in with brown hot blue neutral, brown to the fuse. then to the switch. Neutral appears to also be switched using DP switch. Then both leads go to the primary side of the transformer. There are 3 wires from the secondary It appears to be a +18 -18 with the black (center tap) going to the ground side of the power supply filter caps. 

So that would mean an +18 -18 volt power supply... PLEASE Try to verify this with a schematic I'm looking at this with a photo and bad vision .  or have a tech check it that can verify this with the higher European mains' voltage.

143
I wouldn't use the same cable. I would change to 3 wire ground. Also the European cable may use a lighter guage thane needed as the voltage was higher. I'd use 3 conductor 18  for this amp. Cutting up an old computer cord would do.  Make sure the switch fuse etc is on the Right wire  (as you look at it when plugged in) (so it is polarized properly).

The fuse also as said will have to double due to lower voltage for same watts.

144
If that worked then the contacts on those jacks probably are either dirty or have lost tension holding the switches closed when not used. This is a common problem in a lot of amps.

Fixing it would mean changing the two switched jacks.
If you don't use them you could probably just leave a jumper cord installed there for now.

145
Just another thought the reverb and tremolo pots MAY be different because SOME tremolo pots are reverse pots on some amps (reverse logarithmic) ...at least in vintage tube amps they are.

146
on the 150 W I remeber them from the sears catalogue  it was always peak.

Guy in my band had 100 watt silvertone TUBE and it was much weaker than my Princeton Reverb.
I had a base amp from silvertone too that was much weaker than the (100W) would indicate.

(this was in the 60s)

147
The Newcomer's Forum / Re: Sears 450G amp
« on: April 29, 2010, 09:08:54 PM »
thanks: tip31and 32 check good as does an other transistor.  (PN 3568) there are two others with only markings as 20458R and 20458M (haven't figured out what they are yet)that seem to probably be OK, they test exactly the same with leads lifted. The 2 2n4403 seem to be bad  they test differently from each other they are also the ones that had loose heat sinks...maybe loose enough to contact a leg (clip on heat sinks).

Haven't checked the power supply yet,  will be next week when Postal brings some parts..had a pigtail fuse and I don't have any or an extra fuseholder either.

Have to do almost everything by mail here...the only electronics supply within 100 mile round trip is a radio shack!

I order everything from Tempe (antique radio supply)

Between now and then I'll try and build a schematic/layout diagram

got plenty do do in the meantime on a couple of other amps...but they are tubes and I am actually more in my element.  .....I have seldom had to do anything to my SS amps.

I had to fix my Ampeg G212 when mice ate some wires! >:(
Had to replace tube driver transistors on my Peavey Heritage (hybrid)twice in 20 years.
Filter caps in my Traynor 6400 (mixer amp)
Changed output transistors on Peavey Citation Mark IV once in 20 years
Same on a Peavey Musician
My latest SS is a Carvin SX200 and I anticipate years of not doing anything to it! :D

I usually play/record about 20 hours or more a week.

148
musicparts.com has that schematic plus other info

I quote:

Sears 1465 Silvertone (Chassis 185.12011) Amplifier Service Manual
Contents: Schematics, Controls, Functions & Theory of Operation, Voltage Check Points, Front / Rear Panel Illustrations, PC Board Layout, Speaker Wiring Diagram, Parts List (D1960's) ($15)

I've gotten several hard to find schematics from them. This should give you the values so you can substitute!

149
The Newcomer's Forum / Re: Sears 450G amp
« on: April 28, 2010, 06:12:11 PM »
I was mistaken acutually it was tip31 and 32 pair. I found two bipolars connected to those resistors that checked bad and are probably the problem they had heat sinks that were loose. I'll have to order some next time I order parts.

I actually got the thing for the 16" chassis for an 18 watt Marshall copy head I'm building I want to use in my new album but...I just loaned an Ampeg G212 (130 Watts ) to my grandkids for their keyboard practice! Need to get them something smaller to save everyone's hearing! Getting a reading of 6 and 10 ohms on the resistors even though they look barbecued. So I'll sprout for the two resistors two bipolars and a fuse and see what happens.

150
The Newcomer's Forum / Sears 450G amp
« on: April 27, 2010, 04:14:31 PM »
New here hello all.

I have a Sears 450G amp broken that I bought on ebay. I actually bought it for the chassis which I intended to use for a Single ended tube project as it was just the dimensions I was looking for. (and cheaper than a blank had the right front panel setup.

I'm now thinking I may fix for a practice amp this as My smallest SS amp is a Carvin SX200, (for that matter my lowest power amp is a peavey heritage twin  in low power mode) 

(I'm buried in high power amps and no low power which is why I'm working on building an el34 and a SS practice amp built.)

I was wondering if anyone had a schematic or had a Sears 450G as the power amp board has two burnt unrecognizable resistors.  Power transistors are a tip32/32 pair

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