Sears 450G amp

[bry melvin]

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

[J M Fahey]

Doubt it as a Sears is by definition the generic of the generic, unless somebody is an authorized Sears service technician and has access to that info.
Anyway it looks very simple, maybe you can trace and hand draw it in a couple of hours; then it will be easier both to guess the value of those resistors and help you.
Other option is to measure the single supply DC voltage you have there and slap a TDA2030 or 2050 there.
The preamp should work.

[bry melvin]

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.

[J M Fahey]

How do the TIP31/32 measure up? I would bet they are shorted ; just in case I would replace all ¿5? transistors.
How much does the Power Supply supply? :lmao:
If you post a hand drawn schematic it will be easier; it looks very simple.

[bry melvin]

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!

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

[bry melvin]

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