6au6, 6ar5

a fine line between stupid and clever

Postby dragongoff » Sun Oct 28, 2007 1:23 am

erichayes wrote:The guy who has the amp is out on tour and his wife can't find it, so I'll just have to wait until he checks in. Almost all of those amps were built by Original Equipment Manufacturers (OEMs) like Matsushita, Hitachi, Toshiba, Trio etc for second-steppers like Lafayette, Western Auto, Radio Shack etc, who would put their brand names on them and sell them "exclusively". Usually, the only differences between amps of the same OEM were the speaker size and whether or not it had tremolo.

When I spoke of leaky coupling caps, I was referring to electrical leakage, although those particular caps did leak physically as well. If, indeed, the amp led a benign life, there might not be that much heat damage and the caps could be good to go for a while. The resistors, on the other hand, are losers out of the chute. I had some NOS I picked up at a hamfest that were all over the map--high, low, and one or two that were dead on.

For replacement caps, I'd use either SBE Orange Drops or Illinois metallized polyprops. Xicons are OK if you're on a budget, but I don't know what long term heat effects there might be.

For resistors, I use Xicon small size metal oxide or NTE 2% flameproof (also metal oxide). MO can handle the heat much better than carbon film or composition resistors do, and they don't drift with age. A small size 1 W MO is virtually the same physical size as a ½ W composition, so there isn't a space issue.

The rubber band effect is the result of an incompetent, lazy or inexperienced tech doing a half-assed repair on a piece of equipment, causing it to snap back into the shop until the job is finally done properly.


Eric,

Thanks for the cool info. Perhaps then Matsushita built this Kawai as it's the brand on the speaker.

How much will the sound change if caps and resistors are changed? Is there such a thing as dialing in resistors and caps on an amp, even if the values are the same as the original? Handpicking the parts, as it were, trying them in the circuit to see the effect? Is there a way to tell sound wise if parts need changing?

Goff
User avatar
dragongoff
 
Posts: 6
Joined: Fri Oct 26, 2007 5:09 am

Postby erichayes » Sun Oct 28, 2007 5:23 pm

Generally, in little amps like this, the type of component material has less to do with the sound than how far its value has gone out of spec. Since the amp seems to be working, listen to it and thoroughly familiarize yourself with its sound at various loudness levels. Then have it checked out to see if there's any hidden problem. Any suspicious or defective parts should be removed and their actual values recorded for future reference. Rather than replace the part(s) at this time, a 1" bare 22ga wire should be inserted and soldered into each of the holes the old part occupied. This will allow new parts to be "tacked" into the circuit without disturbing the board.

First step is to tack in values that are the same as the old parts' marked values and listen to the amp. If it's changed--and you like the original sound more than the new sound--go to the resistors and, one by one, replace them with ones that are as close as possible to the actual measured values, listening after each change. If there isn't a noticeable change, reinstall the original value replacement resistors and move to the capacitors, doing the same routine with them.

Usually, the components that affect the sound most in a properly operating amp are the tubes. Unfortunately, these little amps have tube complements that don't lend themselves well to tube rolling. You can try different brands, bearing in mind that Zenith and Sears (Silvertone) did not make their own tubes at all, and the actual manufacturers often bought from each other. The 6AV6s can be drop-in replaced with 6AT6s. Try mixing and matching, as well.

6AR5s were much more popular in Japan than in the USA, so your options are even more limited as far as different brands are concerned. But all hope is not lost. If its socket has nothing going to pin 7, you can plug in a 6AQ5 directly. If pin 7 is going to ground, the trace will need to be cut--carefully--with an xacto or sharp box knife. Make two parallel cuts about a 16th of an inch apart. Then touch the tip of a fine tipped soldering pencil to the cut portion and slide it away from the rest of the trace. Now you can plug in not only 6AQ5s, but all of its military and commercial brethren: 6005, 6095 and 6669. You can also try cousins 6DS5* and 6HR5**, and its renamed brother 6HG5.

*Check power transformer for overheating
**Check tube for glowing plate--not good
Eric in the Jefferson State
erichayes
KT88
 
Posts: 987
Joined: Fri Jan 23, 2004 9:01 pm
Location: McKinleyville CA

Postby jlaney » Sun Oct 28, 2007 5:37 pm

I would replace the coupling caps and any electrolytic caps first. I did just this with my '66 Ampeg B15 a while back. I used Orange Drops to replace the original Black Cat coupling caps, and Sprague Atoms in the bias circuit. Afterwards, the sound tightened up noticeably. For other caps and resistors, I generally wouldn't mess with them unless they look damaged, or the amp needs a specific repair.
jlaney
 
Posts: 8
Joined: Mon May 07, 2007 11:18 pm
Location: Seattle, WA

Postby dragongoff » Mon Oct 29, 2007 12:05 am

Really great info and advice eric and jlaney... I'm sure to keep these in mind regarding this amp and others as well. Glad I found this forum and became a member.

I saw some Tung Sols 6AR5's being sold some where and some Sylvania 6AV6's. I'm really into this different tube combination.

All my other amps, Marshall JCM 900, Marshall Slash, JTM 30, Bassman 50, Dual Showman have the same type of tubes except for the Slash and JTM30 which have EL34's power section. So this 6AR5 amp is a departure from the lot.

Is the use of the 6AR5 in Japan because it's leftover radio tubes? Is there a sound type they were after or just using parts to supply a demand for small amps back in the day? What was the reason for these types? Did any American amps made in USA have similar tube configs at that time?

And who made Silvertone for Sears?
User avatar
dragongoff
 
Posts: 6
Joined: Fri Oct 26, 2007 5:09 am

Harp Amps Silvertone Site

Postby EWBrown » Mon Oct 29, 2007 9:21 am

These were made by numerous suppliers. The "Harp Amps" site is a good place to start:

http://www.harpamps.com/silvertone/ampgallery.html

HTH

/ed B in NH
Real Radios Glow in the Dark
User avatar
EWBrown
Insulator & Iron Magnate
 
Posts: 6389
Joined: Wed Mar 19, 2003 6:03 am
Location: Now located in Clay County, NC !

Re: Harp Amps Silvertone Site

Postby dragongoff » Mon Oct 29, 2007 9:45 am

EWBrown wrote:These were made by numerous suppliers. The "Harp Amps" site is a good place to start:

http://www.harpamps.com/silvertone/ampgallery.html

HTH

/ed B in NH


Thanks.. nice site...
User avatar
dragongoff
 
Posts: 6
Joined: Fri Oct 26, 2007 5:09 am

Kawai guitar amp.

Postby 4-CHANNEL » Tue Feb 26, 2008 8:12 pm

This kind of product is designed for practice only, not for show!. It was manufacturered by Japan, their purpose is for guitarist to listen to the sound effect and reproduction. Matsushita doesn't made these stuff, Only Kawai bought the speaker.

There still room for modification, such as change the power tube to 6bq5,then you will get 5.7watts. Then again monitor the temp. on the power transformer.

_____________________________________________________
Suggestion is for reference only, no liability or responsibility ;) Yellow_Light_Colorz_PDT_20
User avatar
4-CHANNEL
 
Posts: 22
Joined: Mon Feb 25, 2008 7:30 pm
Location: a place near heaven

Postby 4-CHANNEL » Tue Feb 26, 2008 8:39 pm

[quote=

When I spoke of leaky coupling caps, I was referring to electrical leakage, although those particular caps did leak physically as well. If, indeed, the amp led a benign life, there might not be that much heat damage and the caps could be good to go for a while. The resistors, on the other hand, are losers out of the chute. I had some NOS I picked up at a hamfest that were all over the map--high, low, and one or two that were dead on.

For replacement caps, I'd use either SBE Orange Drops or Illinois metallized polyprops. Xicons are OK if you're on a budget, but I don't know what long term heat effects there might be.

For resistors, I use Xicon small size metal oxide or NTE 2% flameproof (also metal oxide). MO can handle the heat much better than carbon film or composition resistors do, and they don't drift with age. A small size 1 W MO is virtually the same physical size as a ½ W composition, so there isn't a space issue.

The rubber band effect is the result of an incompetent, lazy or inexperienced tech doing a half-assed repair on a piece of equipment, causing it to snap back into the shop until the job is finally done properly.[/quote]

The component you suggested for improvement I don't think it worth? no commitment between the product and the component value!!! It would better to buy another amp. rather than invest money on an old equipment.

_____________________________________________________
Suggestion is for reference only, no liability or responsibility ;) Yellow_Light_Colorz_PDT_20
User avatar
4-CHANNEL
 
Posts: 22
Joined: Mon Feb 25, 2008 7:30 pm
Location: a place near heaven

Previous

Return to guitar amps

Who is online

Users browsing this forum: No registered users and 9 guests