first guitar amp repair .dart alamo .

[Tom_Hull]

hi ..

this is my son inlaws amp.
 so heres the problem . its an alamo dart

NO fuse
No transformer
electrifying guitar . reverse plug in cord

SOunds fine at first then there is a loss of volume and a hum when the guitar strings are touched .

not sure how electrifing it is as they are playing on rubber mats.
 

I have two old trans formers 118 ac in and 127 ac out ..7 volts heater wires  no cts on either
i was thinking of useing the transformers i have .

now i need a list of parts .

can you help me so i do not blow this ..

tom

there is powder on the main capacitors
you  may need to veiw this at 75 % veiw





the electronic capacitor 10mfd is 25 volt rating ,,,,,,,,,,,,,,not 25 volt ceramic capacitor .

[tubenit]

Perhaps the camera angle is throwing off what really is there .............. ????

But I am concerned about what looks to be a bare wire going to the B+ positive end of a filter cap that is laying across a transformer.

IF that is voltage going thru that bare wire and it touches the chassis thru that transformer frame, that will be dangerous or deadly, IMO.

With respect, Tubenit

[Tom_Hull]

hi

thanks for your reply ..

i did tell john not to use that amp..  i also ask if he had good life insurance ..uppp.


the wires were just hanging .but not touching
the caps were glued to each other .with those long bare wires .

I will make something alittle better to hold  those tobe fixed wires and caps

but this is what i found ..a resistor wire from the intensity pot melted threw the coated wire . the rolled paper shows the spot melted looks like it was melted when the resistor was first installed ..

could this have been the problem ???,if it was not touching,, it sure was close its a bare spot now..the amp would hum after starting to warm up ..
 tom

[Tom_Hull]

hi . so this is what i am thinking for the transformer

the heater wires for the transformer ......Can i just cut them and leave them out of the circuit ..??????
if i need to hook them up to make a ct do i need lamps or resistors ?????

would this be safe .......
   ohhh fuse first then the switch ..... right

[kagliostro]

There is something strange on your diode connection ...............

Kagliostro

[Tom_Hull]

hi

not sure whats wrong .with the diodes maybe not in series ..



wel now that the short was found .. maybe ....so

i put the capacitors on a board and fixed the bare wires on positive ..

put the amp together and turned it on ..


well there was still a volume fading problem ....and NO HUMMING ... yes ..
yes

that means this amp was always broken most of its life so far.. .. must not have been used much..

now the fading problem  ...

checking through the tubes it turns out there is loose  socket connections .....pushing a tube on its side made contact and now the amp works just dandy..

but now


no fuse

or tranformer

buy new parts for this is ok ..like a PT .

not sure what to do ..


tom

[birt]

i wouldn't try rearranging the circuit for a real PT as used in other guitar amps. instead i'd install an isolation transformer (permanently!) somewhere on the chassis or elsewhere in the amp.
and ground the chassis while you're at it.

[kagliostro]

Yes, the same as Birt

Copy the schematic as is and rebuild the parts that need to be fixed better

the circuit use a 35w4 that is a single diode rectifier with 35v filament heater

also the power tube, the 35c5 has 35v filament heater

the other two tubes have 12v filament

and all filaments are in series

so with a 120v/120v transformer or with two transformers back to back

120v-12v/12v/120v or other that has 120v primary and the same secondary (es. 120v-18v/18v-120v)

you can solve the problem

if you can also install an IEC intake

if your amp sounds like this is very nice

Alamo Dart

Kagliostro

p.s.: please post your schematic a new time, only the part in the down left corner, thanks

[PRR]

> my son inlaws amp.

Your daughter may be very annoyed if this guy dies, and annoyed at you if you had a hand in it.

> they are playing on rubber mats.

ALL the time? Never touching other electric gear, radiator, concrete wall?

Even trained high-voltage technicians sometimes get out-of-bounds and die.

Death is not certain but IF it happens there's the smelly body, EMT tracks in the lawn, questions, forms-forms-forms.....

Do NOT build DC rectifier and heater supply. It already has them. Funky, but that's part of the "tone".

All you need, what you MUST have, is a 120V:120V isolation transformer AND solid bonding from metal chassis to wall outlet 3rd-hole.

> old trans formers 118 ac in and 127 ac out ..7 volts heater

Old? How old? How much is your daughter's man's life worth? Even if SiL isn't worth $5 alive, it's worth $20 to keep him the way he is.

However on today's higher wall voltages, this may be OK. Put a good 3-pin cord to the _127V_ side. Take the 118V side to where the present line-cord is. AND take the linecord Green to a solid chassis connection.

> a loss of volume and a hum

Main electrolytics should be fresh. All dubious connections cleared down to rusty/tarnished metal, scraped, fluxed, tinned, and re-done so as the solder really wets the metal. Someone has replaced most of the small parts, but (after installing iso-trans!!) check for voltage at 35C5 G1, which means the coupling cap is leaking.

[Tom_Hull]

where to get the transformer for this dart alamo.
checked around town but nothing ..120 to 120 50va .. i believe .??




birt.

seems to the best thing a new transformer.



 kagliostro

that schematic is not perfect and i could make sure its as the amp is made .. tomorrow
but heres a cap connection correction .the intensity pot center connection the cap goes there and not connected to the connection beside it ....
any ways tommorrow...heres an fixed sch


PPR

yes never get on a womans wrong side..
but i gave him those bumblebee caps and now maybe he loves his guitar more then my daughter.
i heard this over the phone .she does not mind him playing all the time now,but mom.his gone downstairs to play the guitar again ..
john slow on quiting aself jam for supper ,,ha ha

john sayes its the best gift in his life...funny

he jams at home and at my house ,,,,,its fun

johns so scared to touch anything now ..he has been shocked really good ..

they are old like tube dayes .. iwould rather be able to put in a new  iso transformer .

neat idea about useing the reverse connections on a tran,,looking a  bit...... voltages for a lees paul amp later is running from 105 volts to 125 volts .. neat

i covered over the caps because i just could not leave it like that .


i plugged it a microphone . i do not have a guitar .

the amp is very quiet. at full volume there is almost no hummming at all ,,no crackling .no fading .
it all works ,,tremolo,, intensity ,,speed,, tone ,,volume..
now its hasnot had a guitar pugged in it  yet..

and i need to report on the cost ..to john

elec  caps
tranny
resistors ?/
cap s
ill need a new multimeter ,,buggers  it s dieing

thanks for your interest and time ,, tom

[Tom_Hull]

hi..

 would this be ok as a iso trans former for this amp..????
$13 ........to save a life ..


Transformer; Isolation; Pri:115 to 230VAC, Sec:115VAC; 50/60Hz; 50VA; 1500Vrms
Mfr. Part#:N-68X
Allied Stock#:70218526

http://www.alliedelec.com/images/products/datasheets/bm/PARALLAX/70218526.pdf
tom


tom

[Willabe]

Hi Tom,

Transformer; Isolation; Pri:115 to 230VAC, Sec:115VAC; 50/60Hz; 50VA; 1500 Vrms

I think you're trying to say, that the PRI. is either? PRI:115 or 230VAC, Sec: 115VAC? (Yes apples to oranges.)

The link does not come up for me.

13 bucks to save a life,   

             Brad      

[kagliostro]

Primary 115v+115v (connect it in parallel - BLK with RED/BLK - YEL/BLK with GRN/BLK)

Secondary 115v 435mA (RED - RED)

Shield (WHITE connect to ground)

That is fine

Kagliostro

[Tom_Hull]

hi

here are the specs

N-68X
Electrical Specifications (@25°C)
1. Maximum Power: 50 VA
2. Input Voltage:
Parallel: 115V@50/60Hz
Series: 230V@50/60Hz
3. Output Voltage: 115V + 5%
4. Full Secondary Load: 0.435 Amps RMS
5. Voltage Regulation: 15 % TYP @ full load to no load
Description:
The N-68X is power transformer for isolating equipment from direct connection to the
power line. It is constructed with nonconcentrically wound coils. The primary and
secondary are wound on separate arbors, then assembled on a laminate core
side-by-side separated by insulation. This prevents electrical connection under
normal or overload conditions between the primary and secondary windings.
Safety:
These units are designed with 1500V isolation between winding to winding and
between winding and core. Materials and construction are rated for Class B



i cleaned her up...
i noticed that the rating on the front panel sayes 40 watts ..so i think that means  40 va

and the iso  trans former sayes .435 amps rms

to order caps and resistors it s  about $25 minimun  charge fresh caps
i could put in new carbon resistors ....
the rest of the order i'll fill in for my daughters bass amp. i alll ready have the all the transformers from doug.

i talk to john and he sayes to order everything i need or just give him the order and he will take care of it ..
the amp iwas bought from  an estate sale and was in    grandma's closet .. it was sittting the for more then 35 years in a closet ..

she looks beautifull now . rather then that grey old look

here she is ..light as a feather .and had a good sound even before fixing it ..15 1/2  x 19  x 6 3/4 inches,,,,,,,,,, chassis face plate is 2  x  13 1/4 inches

i am
 tired today i only copied the schematic from the original..
ill post the prove read schematic later .
tom

[PRR]

> ..light as a feather .

Seems to be the high-class kin of my Kent.

[Tom_Hull]

hi PRR

that amp has to be lighter then this one ..

the dart
She's pretty .. maybe ill build a dart  .. but not sure for who or why ..am I   normal ???

 i added a fuse holder ,,and label ,i taped the fuse holder so no body could touch the power line

,the cord holder had a big piece of wood holding some handles   ..that person had only long screws maybe .
change the screw length and I srcew the cord holder in as you can see.

.i also cut part of the wood holding the chassis for the fuse to keep room for the transformer.just incase i need the room .

 it was plywood and nice plywood solid with no voids ..

that kent only 2 screws funny ..,,,when i seen speakers for a electrohome stereo with the speakers bolted to the front sounding board .the fat nuts with a tube as the female end .and a bolt ....


THe schematic is not right so ill go threw  that today ,, not so tired today..

tom

ps i noticed that I need  to keep the electric cord down and not hanging ..I'll attach the electric cord to the bottom of the speaker box near where the cord is wrapped ,,,

so that now the cord will be held in two places ,and maybe less chance of being pull out or tripped on ..

when the parts come in ill have everything ready for simple replacing .. yaaaaaaaaaaaaa   wishing i could play an insturment instead on records and now i have a few organs to learn on .. just haveing  funn.

[Tom_Hull]

hi
Dart alamo schematic ..

here is the probed and checked circuit..dart alamo schematic ..if you see a problem with it then ill check again .the red and orange were hard to distinguish from each other
and the batteries in my meter are just getting used up quick,,

the was no real schematic so I had to do this ..

 now lets hope I never need to bring this schematic to work on her again ..

tom