Marantz 7T Restoration

[jstang]

Sid did not have benefit of the large audio film caps we have today.... The resistors in the 7t were and still are very good. He only had the early not so great sounding low voltage electrolytic caps from the 60's. Ours are better today...

So, I am sure he would have at least tried some of the better caps we have today.

Johnk

 

[USMC Spike]

So are the ionetics the resistors that are the Takman Rex Carbon must be film?

What is the black board material? Phenolic/Paper Resin?

Good luck and enjoy.

 

[CohibaJoe]

So are the ionetics the resistors that are the Takman Rex Carbon must be film?

What is the black board material? Phenolic/Paper Resin?

Good luck and enjoy.

Not touching the Ionetics. I am replacing the other resistors with Takman REX Carbon (Pink).
What I am finding the Originals resistors are coming apart. Seems to me a manufacturing
issue??? I never seen this before in other gear that I have working on.

 

[USMC Spike]

CohibaJo: Okay, I wasn't sure which and I see them now.

They are supposed to be good.

In manufacturing it's a tough go one bad batch from a supplier.
There might be a few other amps within the same SN group.

who knows what happened maybe baked incorrectly or not welded
or something in the process wasn't correct. It happens.

Heck, even a coffee break can result in things not getting
done right. I had a minty minty late 60 early 70s Fender Vibrolux Reverb
amp that for some reason on the reverb return amp a key eyelet was
never soldered...from the factory...thru dealer and buyer...etc.

It was why it was so minty minty that reverb would have strange intermittents
and so it sat in the back of a closet for decades. I forget how I came by it,
either it came in for service or someone had it and sold it cheap cause it
looked good but didn't function well or we traded service on other gear
for it...something.

That fix along with cap change and speaker change ended up being the best
vibrolux most folks had heard. I got talked out of it when a buddy of mine,
also a customer, had is Blackface Deluxe Reverb amp that I did for him
got stolen from his truck in the parking lot of a tiddybar that he went to.

I still miss that SFVR amp to this day. It was a reference amp that I no longer have.

Generally, never sell your references...you'll never find another.

Didn't mean to drag this on.

Cheers,

USMC Spike
Have Gear Will Trade

 

[jstang]

Steel and used as a ground shield.

What is the black board material? Phenolic/Paper Resin?

Good luck and enjoy.

 

[USMC Spike]

CohibaJoe,
You might want to pull the board and either remove and replace
that wire. I think it has exposed wire and could arch and cause
problems down the road.

It's the lead wire in post #20, I can see insulation is melted through to the wire.

LINK

Is this from the repair guy?


HINT:
If glueing caps or other parts to a board,
clean board and cap first with ISO.
Then, orient your cap they way it will lie in your circuit.
with proper lead dress, service loop, etc.
Turn the part over and apply your hot melt,
silicon or other stick and hold material in thin line
and only to the place that actually touches the board.
As Ron Popeil say's "set it and forget it."

Come back later and solder your lead wires.
You can use masking tape to keep the part
from moving while glue sets.
In this way you avoid an unsightly mess
and most of the glue is hidden--Professional looking.

If your tech did this work, I'd find another tech.
No offense to any one here but we should call
them as we see them and our goal is also to
learn and to educate it cannot happen with out
pointing out errors and recommending better
practices.

NOTE: That is not "Bitter" practices.
Once a teacher always a teacher I reckon.

Stress Relief Example (see attached):
Here's an example of the stress relief for a
component. It's not the 7T, look at the diode,
the radius curve bent around the terminal with
the yellow and orange wire.

Non-Examples are shown in the link (post #29 and scroll to post #35):
LINK

 

[CohibaJoe]

CohibaJoe,
You might want to pull the board and either remove and replace
that wire. I think it has exposed wire and could arch and cause
problems down the road.

It's the lead wire in post #20, I can see insulation is melted through to the wire.

LINK

Is this from the repair guy?


HINT:
If glueing caps or other parts to a board,
clean board and cap first with ISO.
Then, orient your cap they way it will lie in your circuit.
with proper lead dress, service loop, etc.
Turn the part over and apply your hot melt,
silicon or other stick and hold material in thin line
and only to the place that actually touches the board.
As Ron Popeil say's "set it and forget it."

Come back later and solder your lead wires.
You can use masking tape to keep the part
from moving while glue sets.
In this way you avoid an unsightly mess
and most of the glue is hidden--Professional looking.

If your tech did this work, I'd find another tech.
No offense to any one here but we should call
them as we see them and our goal is also to
learn and to educate it cannot happen with out
pointing out errors and recommending better
practices.

NOTE: That is not "Bitter" practices.
Once a teacher always a teacher I reckon.

Stress Relief Example (see attached):
Here's an example of the stress relief for a
component. It's not the 7T, look at the diode,
the radius curve bent around the terminal with
the yellow and orange wire.

Non-Examples are shown in the link (post #29 and scroll to post #35):
LINK

Point taken and Corrected...Thank You...The Tech is always looking to better one's restoration techniques.

As with the heats marks...Liquid Tape to cover the areas.

How the parts are being removed are going back with the Bends to the Leads. The exposed leads are from the Original built.

The PrimaLuna that I own uses Point to Point wiring..2017 not 1968. Maybe not a thought at the time to use covering on the wring ???

 

[jstang]

Arcing In a 7t? It's low voltage solid state..... Nothing is going to start arcing except maybe the AC power cord and this is doubtful..... It's not a tube amp or tube tv...

Nothing is melting wires in there except a soldering iron.... Only thing that might melt something is the pilot lamp if left out of its holder.

While it is point to point wiring... The 7t is very very different than a tube unit....

It was designed to a very different set of requirements. Thinking of it like a tube unit is a mistake, it's solid state, built to point to point requirements for solid state.... Which makes it very misunderstood....

Many people make the mistake of applying tube requirements to it...

The supply is 35/37 volts.... The current draw is .032 A AC.

Compared to 400 Vs and 1 amp idle current for a tube amp....or thousands of volts for a Tube TV.


For a minute imagine that the 7t was printed circuit board based.... Would you remove every component and insulate its leads with "corona dope" to prevent arcing to a near by component.... No... Because it is low voltage.

Need to stop thinking of the 7t as a tube unit.... It's solid state.

 

[jstang]

Another thought.....

Some people prefer the sound of BARE WIRE over INSULATED WIRE..... ( let me know when you back to back test that one...I have never....)

Noodle on that one.....

Here is a hint..... Insulation is a "Dielectric".

What is one of the key components of a capacitor?

That's right... Dielectric....

Noodle on that one for a wire..... I mean a while.....

If you look in the 7t, there is more bare wire being used to carry signals and power than you will see in almost any unit..... Especially in the earlier units.

Do you think that was lost on Sid Smith? The 7t has many many hidden engineering gems placed there by Sid...don't mess with it too much. So does the 7C, which is tubes.....

It does have a few limitations and the 1960s low voltage audio path electrolytic caps are the main ones...

johnk

 

[USMC Spike]

CohibaJoe,

That looks good, nice and neat. Minimal other stuff too.
I enjoyed the amp pic. Looking for my own 8b amp,
or I could find the audio research SP3A1, and take
a pic of it. I need to see why the right channel is
off a bit. But that is for another day.

Why is that guy discussing tube amps, because you posted a
pic of an amp?

The 7t is very very different than a tube unit....

It was designed to a very different set of requirements.
Thinking of it like a tube unit is a mistake, it's solid state,
built to point to point requirements for solid state
.... Which makes it very misunderstood....

Many people make the mistake of applying tube requirements to it...

Compared to 400 Vs and 1 amp idle current for a tube amp....
or thousands of volts for a Tube TV.

Or, tens of thousands of volts for a vehicle ignition.

Would you agree we should encourage folks to use best practices?

The supply is 35/37 volts.... The current draw is .032 A AC.

I reviewed the schematic and we have a
+43V potential from the power supply.
S/N 15,001 +.

We also have a bit more power though our
AC mains plug at +120V or more vs. the 110V or 118V
so our B+ might be slightly higher than the schematic.

Good news that Marantz anticipated these voltage
irregularities and spec'ed the transformer and pre-amp for
105 - 135 V AC at 50-60 Hz.

CohibaJoe, is your B+ different then 35/37V?
The 35/37 Volts is still potential?

I take it no one has ever had a solid state device such as
a transistor or opamp fail even if they are less than 12V or 15V?

Another thought.....
Some people prefer the sound of BARE WIRE over INSULATED WIRE.....
( let me know when you back to back test that one...I have never....)

Bare wire vs insulated wire "I have never?"
Then why bring it up?

We can talk autos too.
Auto's used to have bare plug wires.
They're only a 12 V system right?

We won't get into collapsing magnetic coil
fields either now because it's beyond the scope
of this discussion.

If you look in the 7t, there is more bare wire being used to carry signals and power
than you will see in almost any unit..... Especially in the earlier units.

Do those include a moon unit too?
Gag me with a spoon.

The 7t has many many hidden engineering gems placed there by Sid
...don't mess with it too much. So does the 7C, which is tubes.

Should we blame Sid Smith for
the resistor ends that fall off the resistors also?

In the mean time If you'd care to share some pics of your
Model 7 pre-amps and discuss the hidden engineering gems
placed their I'm sure we're all eyes and ears.

Please show us Mr. Sid's gems in this circuit.

Please show us the amount of wire
that is bare in the pre-amps too, if you don't mind.

You have brought up some very valid points.

Thanks,

 

[jstang]

Have you ever owned or worked on a 7t? You should buy one... Helps if you have first hand experience, the schematic does not reveal it all....but 43v/41v ( my error) is not going to start arcing any time soon either....even in the vacuum of space. The stock design of the 7t should not be changed due red herrings.

Best practices for high voltage tubes? Or for low voltage SS.

Cars? Don't know how SAE best practices apply to audio gear...yet another red herring. But what heck now that you mention it... The ignition Primary side is 12vs.... The ignition Secondary side is capable of 20,000v.... And early cars had bare metal straps that connected the distributor to the plugs.... When is the last time you drove a 7t through a car wash....?

Buy the way, the high tension power grid , uses no insulation on the wire.... Thousands of volts.... in some cases 100,000 with no insulation .

7t Engineering gems which go beyond just the circuit.... Already mentioned one other when you asked about the board material...and gave the purpose of it...

I am an EE with 35+ years in the field, worked on lots of stuff... Including things that left the atmosphere.... And my share of cars too.... So my soldering iron is likely larger than most’s...

Will leave this thread to Joe.... Why not start your own on electrics design/construction best practices? Should be fun...we can continue the schooling over there... including the failure modes of semiconductors.

 

[USMC Spike]

Have you ever owned or worked on a 7t? You should buy one... Helps if you have first hand experience, the schematic does not reveal it all....but 43v/41v ( my error) is not going to start arcing any time soon either....even in the vacuum of space. The stock design of the 7t should not be changed due red herrings.

You are right, I should not have used "arc". Perhaps short to ground
from exposed insulation next to the steel ground plane?
Yes, it was quite obvious burned via soldering iron.

You want me to work on one, are you going to sell me one
of yours that need updating?

In the pictures shown I didn't see any other exposed runs
of bare wire, that is why I asked you to show us some pics.

So, you make statements then leave?
That kind of invalidates everything you said.

Thanks,

 

[CohibaJoe]

Well....Getting back to the Recap. Parts (Films) will be shipped out Friday.
Let's see what the next batch of threads bring...

 

[jstang]

Early 7t that 100% stock that I own.

If you look closely in the pic.... there are several signal carrying wires that are intentionally bare wire, one example is the signal wires to the output level switch and others.....

They are not the ground returns, they are the signal carrying....intentionally bare wire.

 

[USMC Spike]

jstang,

That is very interesting, thanks for taking a pic of that.
I can't tell form looking I assumed solid, but at points it looks to be stranded?
Are those silver, silver over copper, copper?

What is or what was the reason for that?
or, what affects are they trying to minimize?

The oracle has advised me that there is a 7T in
my future.

Hmmm, now if I can just find one.

Thanks,

 

[CohibaJoe]

Parts are in...Time to complete this. Pics are coming.

 

[jstang]

The skinny wires in the pic are bare signal carrying single solid core.

Why? Think this goes back to dielectric of the insulation increases stray capacitance.

Not sure of the wire type... Never cut it to see the core. Doubt its silver plated. Tin over copper likely.

Again the early versions have more bare wire then the later ones....

 

[CohibaJoe]

Main Output RAEF board 11-1029: 2nd side

Completed this board. I hooked up to a Amp.......This is sounding so nice.

Next is Low Level Amp Board 11-1026

 

[CohibaJoe]

Low Level Amp Board 11-1026

Completed.

 

[CohibaJoe]

OK....The 0.033 Films are on Backorder for 10 weeks.....No problem..Going to finish the other
films in the mean time.