AIMS VTG-105

[maddog55]

So, I inherited an AIMS VTG-105, probably about 40 years old, from my father in law. Very noisy, lots of buzz and hum. Looks to have most of the original tubes. Ordered replacements. Also looks like it has at least some of the original Filter caps. Decided I could replace the caps myself. Old caps were 3-20uf/600v and 1-30uf/600v. Doing some research and looking around the same value of caps are very expensive, around $25 each. Saw on one site that in most cases you could substitute a 22uf/500v. That's what I did. Installed new caps powered on amp, within a minute "pop" one of the new caps exploded. So, looks like I will have to stick to original values. Anyone have similar experience? Advice on where to find some less expensive than 20uf/600v "Sprauges?

[shooter]

within a minute "pop"

caps don't make that sound just cuz you added a couple uF's, they do however make that sound if polarity was wrong, you have a short somewhere.

Do you have a schematic?
meter?
is this a 2 pronger?

[sluckey]

https://www.tedweber.com/ec206-600

https://www.tedweber.com/ec406-600    (use to replace the 30µF)

Ignore the picture on the left of these pages.

[PRR]

Welcome.

> Old caps were 3-20uf/600v and 1-30uf/600v. .... most cases you could substitute a...500v.

This amp ran 620V in 1970. Probably more on today's wall voltages.

I can believe you pulled out 600V caps. However that was very reckless. The plan going around shows STACKED PAIRS of 450V caps, suggesting that at an early date AIMS realized that 620V on 600V caps was a warranty disaster.

While there are other ways to do it, I think the stacked 450V caps is as good as any.

> very expensive

It is a 105 Watt amplifier. Yes the parts are expensive. Have you priced parts for Ferarri or Mack lately? You can't put Corolla pistons in a 475HP racer or gravel truck, it will spit them out.

[maddog55]

Maybe I shouldn't have said "pop" it exploded. Blew itself right out of the amp, all that was left was smoldering pieces. I do not have a schematic but I took photos of how caps were installed before I took out old ones. I was careful to put new in matching polarity. Amp was working before I took out old caps just a lot of buzz and hum. Center one is the one that blew. Attached photo shows old caps.

[maddog55]

PRR

Thanks for the schematic and advice. Looking at schematic, by stacking do you mean running two 40uf/450v end to end? Sorry for the ignorance of my question.

[PRR]

In Hoffman's Store, the likely part will be seven of - 47uf/500v Illinois -or- 47uf/500v FT
http://hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Capacitors

$7 to $9 each, fifty to eighty bucks, and a low shipping charge (fast service!).
_________________________________

There are other cap suppliers. eBay may turn up an anonymous seller offering ten for a buck. Personally I would only buy from a reputable vendor, not a surplus firecracker store. And for this big amp, I would lean to hi-Temp Snap-In caps, even though they won't fit the original layout (build a sub-board). Snap-Ins are now super common in industrial supplies, even arc-welders, whereas end-leg caps are going out of fashion (except in our world).

Digikey has a wide selection (maybe too wide for easy choice). Hoffman stocks mainly Guitar Amp Parts so his parts are likely to fit even in off-brands.

[PRR]

> running two 40uf/450v end to end?

Hand flash-light. For good light we used (before LEDs) a 3V bulb. Batteries are naturally 1.5V. So we had two batteries end to end.

Capacitors don't make power; only store it. Electrolytic caps are naturally good for 450V, maybe 500V if made very carefully. But as you showed, this amp's 620V on a 500V cap makes a mess on the ceiling. We could use two 310V caps in series (end to end). Not a standard rating. And actually the voltage won't split equally, so we need to be generous. Two equal 400V-500V caps series is safe. At 400V I would want to get all caps from the same batch.

Weber's (and others') "600V" electrolytic caps are traditionally two 350V caps in a cardboard sleeve. (Maybe plastic now.) These did work (the two caps in a sleeve were from the same vat and would tend to split the voltage equally). That was valid. But the plan shows 620V. That's maybe too much to ask of a 600V cap, unless you enjoy scraping the ceiling and buying more caps every some years. In a 520V amp, those caps are fine. In this 620+V amp, I think even AIMS realized they needed more voltage rating.

[kagliostro]

Don't remember well ....

there was a tick to stack a low uF and High Voltage value capacitor (low  uF = less expensive)

on a big uF and low Voltage capacitor (low Voltage = less expensive)

as to maintain a reasonable price and have a High Voltage resulting capacitor

???

Really don't remember if this was a trick I've read here on the forum in the past

Franco

[Sonny ReVerb]

You should use balancing resistors when using caps in series. Electrolytics have wide tolerances and may not share the voltage equally.

https://www.illinoiscapacitor.com/pdf/Papers/voltage_balancing_resistors.pdf

I replaced some caps in a Sunn 2000S which is similar to what you're doing.

[maddog55]

PRR,

You stated in your reply "At 400V I would want to get all caps from the same batch. How would I go about making sure all of the caps were from the same "batch"? Again thanks for the advice.

Maddog55

[sluckey]

Buy all at the same time and from the same vendor.

[Sonny ReVerb]

From the voltage balancing resistor document above:

One way to overcome any potential voltage imbalance is to have capacitors with capacitance values within 5% of each other. This would help minimize the voltage imbalance from occurring without needing to have balancing resistors.

Electrolytic capacitors however cannot be easily supplied with tolerances less than 10%. For these types of capacitors balancing resistors should be utilized.

[maddog55]

Okay,
Installed new Filter Caps today. Two 47uf/450v wired in series with 22k ohm 2w balancing resistors to replace the 20uf/600v Caps. Powered up amp for about 15 mins and nothing blew up. How hot should the caps get? The resistors have already gotten a little brown and color coding stripes dark brown.
Also old Caps were glued down with a glue gun, what a mess. Is that normal?

[sluckey]

Filter caps should never get hot! A hot filter cap is a bad filter cap. Unless it's being heated by something else, like a 22K resistor that's cooking! Those 22K balancing resistors should be 220K. Then they won't cook.

[92Volts]

Filter caps should never get hot! A hot filter cap is a bad filter cap. Unless it's being heated by something else, like a 22K resistor that's cooking! Those 22K balancing resistors should be 220K. Then they won't cook.

At 620v and 44k combined resistance for those two, the pair is dissipating (620^2)/44000=8.73 watts. Yeah, I'd say increasing the resistance 10x is a good start!

[PRR]

> 22K balancing resistors should be 220K.

+1

[maddog55]

Thanks to all for your help!

[maddog55]

Question:

*Do filter caps need to be glued down to the circuit board

[92Volts]

Usually not. If this amp was dropped or bumped, would the cap move enough for exposed parts of the leads to short against the chassis or another item in the circuit? If it's fine now, but a broken/loose connection would allow it to move... how confident do you feel in your solder joints?

If the caps don't appear to be able to move in a dangerous way, don't worry about it. If you do feel a need to secure them, I'd try to use zipties or something. Glue is a pain.

[maddog55]

This amp had zip ties at one time. I can see the remnants of them, last person who changed them out glued them down.

Thanks

[sluckey]

So, is it working now?

[maddog55]

Installed new 220k resistors today and all seems good. Next up new 6550 Power tubes on the way and a couple of new 12at7. Seeing on some power tubes that they have already had "24 hour burn in"? Should any new tube have that done already?

[shooter]

Should any new tube have that done already?

should, yes, actual, probably not

[maddog55]

One more cap I want to replace 50uf/150v. Having a hard time finding one. Can I sub a 100uf/350v or what would be best substitute. Looks like the schematic that PRR posted here is showing a 50uf/100v but 50uf/150v is definitely what is installed currently.

[DummyLoad]

One more cap I want to replace 50uf/150v. Having a hard time finding one. Can I sub a 100uf/350v or what would be best substitute. Looks like the schematic that PRR posted here is showing a 50uf/100v but 50uf/150v is definitely what is installed currently.

47uF @ 160V is more common value.

http://www.mouser.com/ProductDetail/Nichicon/TVX2C470MCD/?qs=sGAEpiMZZMtZ1n0r9vR22SmzhV1iNnMtsJGwppihpyw%3d

--pete

[pompeiisneaks]

One more cap I want to replace 50uf/150v. Having a hard time finding one. Can I sub a 100uf/350v or what would be best substitute. Looks like the schematic that PRR posted here is showing a 50uf/100v but 50uf/150v is definitely what is installed currently.

You can yes.  Going up in voltage rating is never going to hurt.  Down is bad.  As DummyLoad said, though, you can sub a 50 for a 47 most likely and keep the voltage rating the same, for less cost.  Up to you.

As for the glue, it depends on a lot of things.  If the amp is going to be used a LOT then those caps leads can vibrate if not glued or zip tied.  OR if it is in any environment where it has a lot of vibration.  If not, then you're likely fine.

~Phil

[kagliostro]

Also is to be considered that ecaps has a large tollerance as standard, so 50 or 47 in practice can be the same thing

Franco

[maddog55]

Thanks again!

[maddog55]

Any ideas on what kind of speakers these are? Out of my AIMS VTG-105 Combo. Watts?

[pompeiisneaks]

If I'm reading the speaker code, its an eminence (67, see here https://www.tedweber.com/more-codes/) 

Seems to be alnico due to the huge square top as well, I'm almost positive, other than that, not sure of the exact model etc.

~Phil

[maddog55]

Of the four in the amp two have small tears. Replace or have repaired, paper cone replaced?

[bnwitt]

It's been about 20 years since I improperly connected a filter cap and had it explode.  That is a sobering experience.    One can typically repair small tears in speaker cones with coffee filter paper and glue from the back side.  Google "fix tear in speaker"

[PRR]

Small tears are small problems. Worst I have seen is when the edges of a slit rubbed and made a "cricket" sound that drove me mad (madder?). Mostly an imperceptible reduction in output.

What he said. I did such stuff before Mr Coffee so I used a couple layers of Kleenex and rubber cement. Front or back; I guess back looks neater. Don't add much mass or you lose as much as you gain (improved air-slap versus reduced cone motion).

[kagliostro]

rubber cement

 

What is its principal use ? I think is difficult to be find on this side of the pond

may be a lot of years ago there was something similar to be used to repair tire air chamber

but I didn't see it in use by many years (here)

is this a similar procuct ?

http://bostik.it/utilizzi/come-incollare-i-profili-laminati-di-mensole-e-tavoli

--

I've seen vinyl glue used to repair speakers (in junction with paper towels)


https://www.youtube.com/watch?v=ttYDUMBEu3A

Franco

[sluckey]

Rubber cement is a very common brush on craft glue. Doesn't harden. Stays pliable. This is probably the most common brand sold in the USA...

https://www.amazon.com/Elmers-BORE904-11-Rubber-Cement-Adhesive/dp/B004LBT370/ref=sr_1_2_sspa?ie=UTF8&qid=1507626935&sr=8-2-spons&keywords=rubber+cement&psc=1

[kagliostro]

Ciao Steve

.... Rubber cement is repositionable .....

forever or only before it dries ?

--

craft glue, craft gives me a lot of different translations ..... I'm not able to understand the correct mean of craft

Traduzioni di craft

sostantivo

il mestiere
craft, trade, job, profession, metier, experience

l'arte
art, craft, skill

le abilità
ability, skill, prowess, craft, expertise, proficiency

l'imbarcazione
boat, craft, ship, embarkation

la nave
ship, vessel, boat, craft, freighter

la barca
boat, craft

il natante
boat, craft

la categoria
category, class, rating, grade, kind, craft

i'inganno
deception, deceit, trick, trickery, guile, craft

la corporazione
guild, corporation, body, craft


Franco

[sluckey]

Rubber cement remains flexible even after it dries. And the parts can be separated again even after the glue dries without destroying the parts. Let's say the leather plies of your belt have separated at the end. I would recommend using rubber cement to glue the layers back together. The belt is now good as new and remains flexible. Use for temporary fix on a shoe sole that has separated.

Or use rubber cement to put your favorite photographs into a scrap book or photo album. The photos will remain securely attached but can be removed later without destroying the photos.

I meant "craft" as in the sense of small crafts and hobbies, such as found in this popular USA craft store...

https://www.hobbylobby.com/

Here's a description for Elmer's rubber cement as found at Hobby Lobby...

"Elmer's No-Wrinkle Rubber Cement is for mounting photos, cut and paste jobs, repairs and more. For an easily removable bond, brush an even coat on one surface and join immediately. To remove, peel gradually, starting at edge. With a built-in brush, this glue can be used in art and craft projects of all areas. Brush it on, and peel it off as needed!"

[bnwitt]

Small tears are small problems. Worse I have seen is when the edges of a slit rubbed and made a "cricket" sound that drove me mad (madder?).

That wasn't the speaker it was Bobby Goldsboro in your shop.  He was famous for making cricket noises and driving people crazy.

[kagliostro]

Many thanks Steve

all is clear now

Franco

[Sonny ReVerb]

http://en.bab.la/dictionary/english-italian/rubber-cement

I think it's the same stuff they use to apply a patch to a bicycle tire. Try a bike shop?

[SoundmasterG]

Any ideas on what kind of speakers these are? Out of my AIMS VTG-105 Combo. Watts?

If you decide to replace those speakers with something else, I would be interested in one of them, working or non-working as long as it could be reconed. I have an AIMS amp with one one speaker and it would be nice to get another of those. Though it depends on if those are 10's that you have there or 12's. I would need a 12 inch.


Thanks,

Greg

[mresistor]

Question:

*Do filter caps need to be glued down to the circuit board

If you do decide to do this I would avoid any sealant that has acetic acid in it  and go with a "neutral cure" sealant or glue.

[pompeiisneaks]

Yeah absolutely, I've found that the GE Silicone II has no acids or other chemicals that can harm circuits, I think it was someone here (maybe PRR?) that told me about this, and I've used it since.  Love it. 

~Phil

[mresistor]

Good stuff Phil ...   btw I got a kick out of this at your website 


"Hello and welcome to our site, please do let us know what you think when we actually have something!"   

[pompeiisneaks]

Heh I've been meaning to actually update that at some point, but have too many things going on at once, I just got myself a small 10x10 cnc machine I need to put together so I can engrave my own faceplates etc. 

So many things, so little time ;P

~Phil

[PRR]

Tire-glue, or shoe-glue, is over-kill.

A long time ago we stuck paper to paper with a thin glue made of raw rubber and solvent. It could be peeled-off easily. Didn't get hard. Did not rot the paper quickly (apparently some formulas may cause long-term rot and decay in photographic prints).

https://en.wikipedia.org/wiki/Rubber_cement

Looks like snot (blow your nose). Stinks. Has mostly been replaced by Glue Sticks (like lip-stick only for sticking paper together).

In the US, that glass jar with brush in the cap is what we expect.


http://en.bab.la/dictionary/english-italian/rubber-cement  -- seems to also mean "mastic", which here is a very stiff rubber+solvent mix for sealing windows etc
https://forum.wordreference.com/threads/rubber-cement.1237200/

"Contact cement", often used to stick plastic laminate to chip-board, is a thicker rubber cement. In cabinets, drying is slow, so you apply, wait to get tacky, then instant stick. You could try that, but it is fairly thick, and we want to build thin layers. Small jar; also sold in half-liter and large buckets for industrial laminating. "Adisivo a Contatto Unversale"?

What is your Artiglio? Is it rubbery glue in a squeeze tube? This page shows Artiglio on a loudspeaker rim gasket. Looks more like leather and shoes than paper, but I guess you can spread it thin, and I'm sure it is handy for many things.

[maddog55]

These are 10" speakers. I opted to use a small amount of silicone.
Thanks for all of the tips!

[SoundmasterG]

These are 10" speakers. I opted to use a small amount of silicone.
Thanks for all of the tips!

Thanks Maddog55! Good luck with the amp!

Greg

[kagliostro]

As Mastice we can call a large kind of glue, not a specific type

The principal difference of usual Bostik with Rubber Cement, is that it is a contact glue and not a removable glue

I never used the Artiglio version, but the image that show it used to glue foam on speaker give me the idea that it isn't removable

also they specify that it is to be used for a perfect and durable joint (so ... no removable) on leather, cork, felt, wood, plastic, rubber

I think it will not be as strong as Tire-Glue, but enough strong to be used for shoes soles

Franco