Date   
Smoking 2465B (Rifa/30-ohm) + Recap = PS will not start

tekscopegroup@...
 

Yesterday was using the 2465B (SN+50K) and a loud POP and a puff of smoke came out the back. After inspection sure enough I spotted the remains of one of the RIFA caps. The 30-ohm resistor in series with it was also toast. I have been putting off the full recap of this scope for a while now, with new Mouser parts waiting in a bag. Since I am on 120VAC (more like 127-129V in my area) I figured I had ample time, although the Rifa caps looked quite crazed last time I saw them when I did the NVRAM/A5 work. So maybe now would be a good time to recap, not just fix the damage.

Full recap, only one cap at a time to avoid mixups or mistakes. The only ones I did not have was the two 2200pf 250VAC, one 0.01uF 250V and one 0.056uF 250V film caps, back then forgot to order them. The two 2200pf look a bit crazed, definitively will replace them asap. The 0.068 Rifas where replaced with 0.1uF X2 300V Kemet Safety caps that where suggested as a better substitute in one of the cap lists.

Also replaced the 4.7uF 10V Tantalum with a fresh 4.7/50V same composition type unit. The 3x 1uF 50V BP caps where also replaced, and the new ones are much smaller, tiny, in comparison to the originals so hope they still are ok to use (Mouser PN 647-UMP1H010MDD1TP in case anyone wants to check). Plus two new beefier 15-ohm 3W AC input resistors, and 2W for the 270K on the power supply. Even replaced the two Sprage main caps with 330uF 250V Radial Nichicons by extending their negative wire to reach the board. The originals still look pristine but since I already had the new ones on hand went ahead and swapped them as well.

BTW, all of the tall blue caps (180uF and 250uF) where more or less starting to leak from underneath, not much residue on the board, but definitively the smell when desoldering some of them was the biggest tell, and all of them had a slight oily residue between the leads. C1111 was the worst offender. All other caps overall looked quite good, have not tested any of them yet.

Before putting the PS back together double-triple checked that all caps where at the right locations, correct value and polarity orientation.

Upon scope power on the fan runs, all the front panel indicators flash only once in unison and then turn off, except for the green Trig/Sweep led staying on. The 3 GPIB Leds stay on continuously. Nothing else happens. Nothing on screen, no trace, nada.

I checked that all cables in/out of the power supply where plugged in correctly: the one going to the A5 is foolproof. The other two connectors on the power supply (the one with the multi-colored cables under the fuse and the other that only has white cables next to it) are properly seated and aligned with the pins on the board. The only other plug gors to J2474 has 3 small cables going towards the GBIB board and it is orientated correctly (printed letters/numbers up). Checked continuity of all the "stab" pin connectors as I understand they sometime can create a loose/intermittent contact if inserted the wrong way. All pins checked out fine.

Here are the the rail voltages at J119:

+15 -> +10.4V
-15 -> -11.7v
+5D -> +4.3V
+5A -> +3.3V
-5 -> -3.5V
-8 -> -5.3V
+10 -> +7.3
+42.4 -> +28.8V
+87 -> +59.6V

Needless to say all rails are way low. I even measured the voltage across the two new main caps on the J231A/B connector and I do read about 150V on each, total a bit over 300V, so I'm thinking that juice should in fact be getting into the PS.

Verified that the voltage selector switch was securely connected to the two bottom tabs, and the wires from fuse holder and line filter go to the remaining two other taps further up the board. Just checked continuity of the voltage selector switch at the tips of the connectors that go into the board and its almost zero ohms as expected (115V position). I would think that if this switch or the wires where not connected properly, the PS would assume 240V input, and with only 120 going in it might create a low voltage situation like the one I seem to be having. But no dice.

At this point I have the PS out again and on the bench, no way to safely poke into it while inside the scope. First thing again checked all the new caps and everything is confirmed correct. At this point was also looking at the PS troubleshooting chart in the SM, and the W1060 test jumper procedure. But it requires a test load for which at this point I don't have the correct specified resistors at hand. BTW just to know, what is the spec of the diode and voltage of the 3.3uF cap used for the load? Manual only provides Tek PNs.

I would think that with the exploding Rifa cap and burned resistor being well ahead of the actual power supply nothing else would have been damaged. Not even the main fuse blew, and I think it was just time for the cap to let go, and not because of an incomming huge spike or surge although could not be 100% sure. But I had my 2247A also turned on and some other equipment at the same time and on the same AC circuit, and everything else its fine. Nothing else around reacted to any abnormalities in the AC line either.

Any words of wisdom as always much appreciated.
Alex

Re: 2465A channel 2 problems

Siggi
 

To diagnose the attenuator relays you can simply measure the DC resistance
while you run up and down the scale. It should be 1MOhm within fairly close
tolerance throughout. If you have bad contacts you'll see non-trivial
deviations from that.

On Thu, Oct 17, 2019 at 12:18 PM machineguy59 via Groups.Io <machineguy59=
yahoo.com@groups.io> wrote:

You should be able to hear the relays switch as you change scales. That
will indicate the logic is operating. It is more likely the attenuator is
dirty and the fingers don't make good contact on the ceramic substrate.
Cleaning is a delicate process to not break the ceramic or bend the contact
fingers. Sometimes you can clear the problem by spraying a contact cleaner
into the attenuator. But the best, long term solution is to open the
attenuator and clean it, OR replace the attenuator. Both are involved
processes.
On Wednesday, October 16, 2019, 06:58:23 PM CDT, GerryR <
totalautomation1@...> wrote:

That's the problem, in the normal mode, the 1, 2 and 5 volt ranges are
all
off, for example, a 1V signal on the 1V per division scale, displays as if
on the 100 mV scale, etc., so I am assuming the attenuator is not
switching
for those ranges, but don't know if the relays in the attenuator, or the
logic telling which tells them to switch that is bad. The digital readout
shows 1V on the 1V scale but the display of the wave is as if it is on the
100 mV scale.
Is there a list of digital words for the different scales or a way to tell
if the logic is bad?

GerryR


----- Original Message -----
From: "machineguy59 via Groups.Io" <machineguy59=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Wednesday, October 16, 2019 6:48 PM
Subject: Re: [TekScopes] 2465A channel 2 problems


How does Channel 2 work when using the scope in the "normal" mode? If it
seems about right (just not precisely calibrated) when measuring known
voltages then the attenuator is switching.
On Wednesday, October 16, 2019, 03:31:47 PM CDT, GerryR
<totalautomation1@...> wrote:

A little history first: Acquired the 'scope recently and everything was
working fine. Old battery dated 07-87. Decided to change battery and took
all known precautions, but somehow screwed up and requires re-cal. I have
attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed
02" which is a limit failure. Channel 2 "calibrates" up to the 10V input
(cal 02), and I get a Limit 130 error, no matter what I try, so I assume
that is my problem. In the non-calibrate run mode, the channel 2 input
only
works up to the 500 mV range (Hi-Impedance input with co-ax) and with the
10X probe, up to 5V. The display range readout works, but in the 1V, 2V
and
5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so
it
appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper
outputs are not getting to the drivers for the attenuator relays, or is
this
still a calibration problem? I have no way to monitor a "word" from the
processor at this point. I did try monitoring channel 1 at the drivers and
comparing them to channel 2, but found it difficult to get any meaningful
data. Any help will be appreciated.
GerryR











Re: 2465A channel 2 problems

 

You should be able to hear the relays switch as you change scales.  That will indicate the logic is operating.  It is more likely the attenuator is dirty and the fingers don't make good contact on the ceramic substrate.  Cleaning is a delicate process to not break the ceramic or bend the contact fingers.  Sometimes you can clear the problem by spraying a contact cleaner into the attenuator.  But the best, long term solution is to open the attenuator and clean it, OR replace the attenuator.  Both are involved processes.

On Wednesday, October 16, 2019, 06:58:23 PM CDT, GerryR <totalautomation1@...> wrote:

That's the problem, in the normal mode, the 1, 2 and 5 volt ranges are all
off, for example, a 1V signal on the 1V per division scale, displays as if
on the 100 mV scale, etc., so I am assuming the attenuator is not switching
for those ranges, but don't know if the relays in the attenuator, or the
logic telling which tells them to switch that is bad.  The digital readout
shows 1V on the 1V scale but the display of the wave is as if it is on the
100 mV scale.
Is there a list of digital words for the different scales or a way to tell
if the logic is bad?

GerryR


----- Original Message -----
From: "machineguy59 via Groups.Io" <machineguy59=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Wednesday, October 16, 2019 6:48 PM
Subject: Re: [TekScopes] 2465A channel 2 problems


How does Channel 2 work when using the scope in the "normal" mode? If it
seems about right (just not precisely calibrated) when measuring known
voltages then the attenuator is switching.
    On Wednesday, October 16, 2019, 03:31:47 PM CDT, GerryR
<totalautomation1@...> wrote:

A little history first: Acquired the 'scope recently and everything was
working fine. Old battery dated 07-87. Decided to change battery and took
all known precautions, but somehow screwed up and requires re-cal. I have
attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed
02" which is a limit failure. Channel 2 "calibrates" up to the 10V input
(cal 02), and I get a Limit 130 error, no matter what I try, so I assume
that is my problem. In the non-calibrate run mode, the channel 2 input only
works up to the 500 mV range (Hi-Impedance input with co-ax) and with the
10X probe, up to 5V. The display range readout works, but in the 1V, 2V and
5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so it
appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper
outputs are not getting to the drivers for the attenuator relays, or is this
still a calibration problem? I have no way to monitor a "word" from the
processor at this point. I did try monitoring channel 1 at the drivers and
comparing them to channel 2, but found it difficult to get any meaningful
data. Any help will be appreciated.
GerryR

Re: 244x 246x Ebay kit discount code PSWEET20

Siggi
 

I get a message "Unfortunately, this code no longer works. Please continue
with your order."

On Thu, Oct 17, 2019 at 11:10 AM M Yachad <@yachadm> wrote:

Barry

I have no idea.

Would you mind doing a Buy-it-now, and insert the Ebay discount code
PSWEET20 on the line just before the total.

You don't have to complete the Buy.

Just let me know if the code reduces the price.

Thanks

Menahem



WTB: Tek 200 series battery holders (caps) x4

KeepIt SimpleStupid
 

Someone on the bay sold me a scope minus the battery holders. They must have been discarded with the batteries.
Four of the caps make up an integral spacer and fit on the end of ends of the two battery packs.
Contact me off list. (East Coast US)
I will entertain overseas offers as well.

Re: 244x 246x Ebay kit discount code PSWEET20

 

Barry

I have no idea.

Would you mind doing a Buy-it-now, and insert the Ebay discount code PSWEET20 on the line just before the total.

You don't have to complete the Buy.

Just let me know if the code reduces the price.

Thanks

Menahem

Re: 244x 246x Ebay kit discount code PSWEET20

n4buq
 

Hmmm. I just opened that link and there's no discount showing. I wonder if that's country-specific?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "M Yachad" <@yachadm>
To: TekScopes@groups.io
Sent: Thursday, October 17, 2019 6:01:56 AM
Subject: [TekScopes] 244x 246x Ebay kit discount code PSWEET20

https://www.ebay.com/itm/252865418970

On my listing, I just noticed that Ebay is offering a $25 discount (Kit +
S&H) on my kits.

Valid until 18th October.

I just saw it by chance - Ebay didn't notify me, and I still get paid my full
price.

That means that they are making money hand-over-fist, if they can afford to
offer discounts like that.

So, courtesy of Ebay, if any of you have been holding back on buying my kit,
take advantage of this discount now.

I'll need to see photos of your A1 A2 A3 A5 A9 (and A4 and A14, if
installed), in order to make up the custom kit.

Menahem Yachad
CondorAudio



Re: Yahoo Groups are deleting all files in December

Richard Tyner <shawneesdad@...>
 

I was not sure if any of the old group files might be be on Yahoo or not. Just wanted to let others know just in case

Re: 2465A channel 2 problems

Chuck Harris
 

Hi Gerry,

First, you are not supposed to get a trace, just a pair
of dots, approximately 10 divisions apart.

This is a crucial step, as it affects all future steps.

I would suggest that you always put it in VAR mode, as it
will always give you an adjustable range to hit the mark.

But note: It is most important that the VAR knob be back
in its click before you start the next, and all subsequent,
steps. If you do not do this, you will achieve out-of-range.

If you repeat this step after having done it recently, you
will usually find that the dots are perfectly spaced.

There is no linkage between the 50 ohm annunciator light and
the 50 ohm relay in the preamp. Unless your preamp is broken,
it is in 50 ohm mode.

As a test, when the scope is in normal mode, put the preamps
in 50 ohm mode, and measure them with an ohmmeter. If they
are other than 50 ohm, you have the ever popular burned out
50 ohm load. Unless you are very clever you will be replacing
your preamp, as the resistor is printed on the ceramic substrate.

-Chuck Harris

GerryR wrote:

Another question or two for those in the know: At the beginning of the Cal 02 procedure, it states to connect a 0.5 V standard-amplitude signal to CH 1 and to use CH 2 Position to vertically position the "trace" to within 1 division of the center graticule line, and then to use the CH 1 Position and Volts/DIV VAR controls to obtain a 10-division horizontal signal. I don't get a "trace," only 2 dots. I can position the dots with the controls to put one dot on the first graticule line and the other on the 10th.
Question 1: "Is this "normal," or am I doing something wrong?" I've read and re-read the procedures and can't find any references to this.

Also, at the beginning of the Cal 01 procedure, it states that, "Upon entering Cal 01, the Input Coupling is automatically set to 50 ohm DC ....." This doesn't appear to be true for the other Cal procedures (2,3,4,etc), as I had to install a terminator on my generator to get the actual levels called out in the test procedures (monitored on another scope).
Question 2: "Is this correct, or am I missing something here, as well?

Thanks in advance for any input!

Gerry

Re: 2465A channel 2 problems

GerryR
 

Another question or two for those in the know: At the beginning of the Cal 02 procedure, it states to connect a 0.5 V standard-amplitude signal to CH 1 and to use CH 2 Position to vertically position the "trace" to within 1 division of the center graticule line, and then to use the CH 1 Position and Volts/DIV VAR controls to obtain a 10-division horizontal signal. I don't get a "trace," only 2 dots. I can position the dots with the controls to put one dot on the first graticule line and the other on the 10th.
Question 1: "Is this "normal," or am I doing something wrong?" I've read and re-read the procedures and can't find any references to this.

Also, at the beginning of the Cal 01 procedure, it states that, "Upon entering Cal 01, the Input Coupling is automatically set to 50 ohm DC ....." This doesn't appear to be true for the other Cal procedures (2,3,4,etc), as I had to install a terminator on my generator to get the actual levels called out in the test procedures (monitored on another scope).
Question 2: "Is this correct, or am I missing something here, as well?

Thanks in advance for any input!

Gerry

------ Original Message -----
From: "machineguy59 via Groups.Io" <machineguy59=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Wednesday, October 16, 2019 6:48 PM
Subject: Re: [TekScopes] 2465A channel 2 problems


How does Channel 2 work when using the scope in the "normal" mode? If it seems about right (just not precisely calibrated) when measuring known voltages then the attenuator is switching.
On Wednesday, October 16, 2019, 03:31:47 PM CDT, GerryR <totalautomation1@...> wrote:

A little history first: Acquired the 'scope recently and everything was working fine. Old battery dated 07-87. Decided to change battery and took all known precautions, but somehow screwed up and requires re-cal. I have attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed 02" which is a limit failure. Channel 2 "calibrates" up to the 10V input (cal 02), and I get a Limit 130 error, no matter what I try, so I assume that is my problem. In the non-calibrate run mode, the channel 2 input only works up to the 500 mV range (Hi-Impedance input with co-ax) and with the 10X probe, up to 5V. The display range readout works, but in the 1V, 2V and 5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so it appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper outputs are not getting to the drivers for the attenuator relays, or is this still a calibration problem? I have no way to monitor a "word" from the processor at this point. I did try monitoring channel 1 at the drivers and comparing them to channel 2, but found it difficult to get any meaningful data. Any help will be appreciated.
GerryR

244x 246x Ebay kit discount code PSWEET20

 

https://www.ebay.com/itm/252865418970

On my listing, I just noticed that Ebay is offering a $25 discount (Kit + S&H) on my kits.

Valid until 18th October.

I just saw it by chance - Ebay didn't notify me, and I still get paid my full price.

That means that they are making money hand-over-fist, if they can afford to offer discounts like that.

So, courtesy of Ebay, if any of you have been holding back on buying my kit, take advantage of this discount now.

I'll need to see photos of your A1 A2 A3 A5 A9 (and A4 and A14, if installed), in order to make up the custom kit.

Menahem Yachad
CondorAudio

Re: 2465A channel 2 problems

GerryR
 

That's the problem, in the normal mode, the 1, 2 and 5 volt ranges are all off, for example, a 1V signal on the 1V per division scale, displays as if on the 100 mV scale, etc., so I am assuming the attenuator is not switching for those ranges, but don't know if the relays in the attenuator, or the logic telling which tells them to switch that is bad. The digital readout shows 1V on the 1V scale but the display of the wave is as if it is on the 100 mV scale.
Is there a list of digital words for the different scales or a way to tell if the logic is bad?

GerryR

----- Original Message -----
From: "machineguy59 via Groups.Io" <machineguy59=yahoo.com@groups.io>
To: <TekScopes@groups.io>
Sent: Wednesday, October 16, 2019 6:48 PM
Subject: Re: [TekScopes] 2465A channel 2 problems


How does Channel 2 work when using the scope in the "normal" mode? If it seems about right (just not precisely calibrated) when measuring known voltages then the attenuator is switching.
On Wednesday, October 16, 2019, 03:31:47 PM CDT, GerryR <totalautomation1@...> wrote:

A little history first: Acquired the 'scope recently and everything was working fine. Old battery dated 07-87. Decided to change battery and took all known precautions, but somehow screwed up and requires re-cal. I have attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed 02" which is a limit failure. Channel 2 "calibrates" up to the 10V input (cal 02), and I get a Limit 130 error, no matter what I try, so I assume that is my problem. In the non-calibrate run mode, the channel 2 input only works up to the 500 mV range (Hi-Impedance input with co-ax) and with the 10X probe, up to 5V. The display range readout works, but in the 1V, 2V and 5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so it appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper outputs are not getting to the drivers for the attenuator relays, or is this still a calibration problem? I have no way to monitor a "word" from the processor at this point. I did try monitoring channel 1 at the drivers and comparing them to channel 2, but found it difficult to get any meaningful data. Any help will be appreciated.
GerryR

Re: Yahoo Groups are deleting all files in December

 

It doesn't impact us at all - we moved over to groups.io lock stock and barrel (including all files and pictures) ages ago.

D.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Abc Xyz
Sent: 16 October 2019 20:52
To: TekScopes@groups.io
Subject: Re: [TekScopes] Yahoo Groups are deleting all files in December

Is that a Good Thing or a Bad Thing???

On Wed, Oct 16, 2019, 12:06 PM Richard Tyner <shawneesdad@...> wrote:

Yahoo has made the decision to no longer allow users to upload content to
the Yahoo Groups site. Beginning October 21, you won't be able to upload
any more content to the site, and as of December 14 all previously posted
content on the site will be permanently removed. You'll have until that
date to save anything you've uploaded.

73 Richard W4MCD



Re: 2465A channel 2 problems

 

How does Channel 2 work when using the scope in the "normal" mode?  If it seems about right (just not precisely calibrated) when measuring known voltages then the attenuator is switching.

On Wednesday, October 16, 2019, 03:31:47 PM CDT, GerryR <totalautomation1@...> wrote:

A little history first:  Acquired the 'scope recently and everything was working fine. Old battery dated 07-87.  Decided to change battery and took all known precautions, but somehow screwed up and requires re-cal.  I have attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed 02" which is a limit failure.  Channel 2 "calibrates" up to the 10V input (cal 02), and I get a Limit 130 error, no matter what I try, so I assume that is my problem.  In the non-calibrate run mode, the channel 2 input only works up to the 500 mV range (Hi-Impedance input with co-ax) and with the 10X probe, up to 5V.  The display range readout works, but in the 1V, 2V and 5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so it appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper outputs are not getting to the drivers for the attenuator relays, or is this still a calibration problem?  I have no way to monitor a "word" from the processor at this point.  I did try monitoring channel 1 at the drivers and comparing them to channel 2, but found it difficult to get any meaningful data.  Any help will be appreciated.
GerryR

2465A channel 2 problems

GerryR
 

A little history first: Acquired the 'scope recently and everything was working fine. Old battery dated 07-87. Decided to change battery and took all known precautions, but somehow screwed up and requires re-cal. I have attempted re-cal, and went from a "Test 04 Failed 04" to a "Test 04 failed 02" which is a limit failure. Channel 2 "calibrates" up to the 10V input (cal 02), and I get a Limit 130 error, no matter what I try, so I assume that is my problem. In the non-calibrate run mode, the channel 2 input only works up to the 500 mV range (Hi-Impedance input with co-ax) and with the 10X probe, up to 5V. The display range readout works, but in the 1V, 2V and 5V ranges, it appears to stay in the 100 mV, 200 mV and 500 mV ranges, so it appears the attenuator isn't switching properly.

Is there a way to tell whether it is the attenuator, or if the proper outputs are not getting to the drivers for the attenuator relays, or is this still a calibration problem? I have no way to monitor a "word" from the processor at this point. I did try monitoring channel 1 at the drivers and comparing them to channel 2, but found it difficult to get any meaningful data. Any help will be appreciated.
GerryR

Re: Yahoo Groups are deleting all files in December

Abc Xyz
 

Is that a Good Thing or a Bad Thing???

On Wed, Oct 16, 2019, 12:06 PM Richard Tyner <shawneesdad@...> wrote:

Yahoo has made the decision to no longer allow users to upload content to
the Yahoo Groups site. Beginning October 21, you won't be able to upload
any more content to the site, and as of December 14 all previously posted
content on the site will be permanently removed. You'll have until that
date to save anything you've uploaded.

73 Richard W4MCD



Re: Yahoo Groups are deleting all files in December

Chuck Harris
 

You know, of course, that tekscopes is not on yahoo? Right?

-Chuck Harris

Richard Tyner wrote:

Yahoo has made the decision to no longer allow users to upload content to the Yahoo Groups site. Beginning October 21, you won't be able to upload any more content to the site, and as of December 14 all previously posted content on the site will be permanently removed. You'll have until that date to save anything you've uploaded.

73 Richard W4MCD



Yahoo Groups are deleting all files in December

Richard Tyner <shawneesdad@...>
 

Yahoo has made the decision to no longer allow users to upload content to the Yahoo Groups site. Beginning October 21, you won't be able to upload any more content to the site, and as of December 14 all previously posted content on the site will be permanently removed. You'll have until that date to save anything you've uploaded.

73 Richard W4MCD

Re: Ths730 alternative to p5102 probe

Chuck Harris
 

For audio use, any bnc probe that can handle the voltage
will work just fine. Look at the P6007 and P6009.

-Chuck Harris

Scott Adams via Groups.Io wrote:

Most of my high voltage measurement needs are in the audio frequency range, I like to repair and build vacuum tube stereo amps.



Re: Ths730 alternative to p5102 probe

Scott Adams
 

Most of my high voltage measurement needs are in the audio frequency range, I like to repair and build vacuum tube stereo amps.