Anyone Familliar With The Dynaco PAT-5?

[NoTransistors]

The problem with buying anything on ebay is that among other things, one does not know the history of the item.
This thing was $99.00 Canadian and has a hastily soldered-in new line cord.
But otherwise, it is in great shape.
The one issue is that the phono stage seems to have waaay too much gain.
Crack the volume just a bit, and it is blasting.
Is this normal, or did a previous owner tinker with it?
It will be fun tracing out everything to find a modification.

 

[TWTRTECH]

What are you feeding the phono input with? In other words is the turntable cartridge a magnetic or ceramic, as old style ceramic cartridges put out a much higher signal level and can overload a phono preamp.

 

[NoTransistors]

It is a Shure ML140HE cartridge. No ceramic or crystal pick-ups in this household.
The preamp has enough gain for a M.C. cartridge.
Two phono inputs. Both have this issue.
The boards might have been played with. Don't know yet.

 

[2chanman]

The Pat-5 manual tells how to vary the gain of the phono stage by changing specific resistor values. Obviously, someone set it up for a moving coil pickup. Change it back to the original circuit values and you should be fine.

 

[NoTransistors]

Thanks.
I'll give it a go tonight.

 

[Sam Cogley]

Even better, set one for MM and one for MC.

 

[TWTRTECH]

Also, what turntable are you using, if it is one of the newer models with a built in phono preamp, then what you would have is line level single being feed to the phone stage of the preamp.

 

[larryderouin]

TWTRTECH; He's got a Dual 1219 w/ Shure ML140HE. Sounds like changing the resistors back to accomodate a MM would work best.

 

[Pio1980]

If I had another one, I'd get an update kit for it for the caps and ICs if nothing else.

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[TWTRTECH]

Also, what turntable are you using, if it is one of the newer models with a built in phono preamp, then what you would have is line level single being feed to the phone stage of the preamp.

Didn't see the bottom signature line. Yes, the Pat-5 needs the Phono Preamp redone.

 

[NoTransistors]

I am glad to see some feedback from my buddies.
The resistors that are meant to be changed for different phono gain are factory value.
All voltages on all boards are spot-on.
The wiring is not too shabby and solder joints, while not to my standards, seem decent. I want to go over them, though.
I see that a vendor on ebay does offer re-cap kits, and even an original I.C. for the tone control. No one appears to offer an upgrade for the I.C..
The assembler did not add load capacitors to the phono section. So I do need to find four 200 pfd caps. Since paralleling caps simply adds their values, I can play with both 200 and 400 pfd loading.
But why does a cartridge that outputs under 5.0 mv play so loud?
I can play with the resistor values, but what I need to know why what Dynaco chose as gain is so off-the-wall.

 

[Pio1980]

Check with Audio by Van Alstine for IC upgrades for the PAT 5.

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[NoTransistors]

I can call Frank. You do know that his favorite hobby is gutting old Dynaco chassis and installing his own stuff?
I have his 'updated' PAT-4 and think that it sounds aweful. But my Van Alstine amp that he built on a Stereo 120 chassis, reusing only the transformer sounds great. Go figure.

 

[Pio1980]

I can call Frank. You do know that his favorite hobby is gutting old Dynaco chassis and installing his own stuff?

So I've heard, good for the PAT-4 anyway. He used to upgrade the Dyna stuff and I dunno if he still does that. He did a PAT 5 and ST 150 for me ca 1978.

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[2chanman]

NoTransistors:

I have used the PAT-5 in several systems and there is nothing excessive about the phono stage gain in it's original "factory" configuration. What may be overlooked here is the gain of the amplifier you are driving with the PAT-5. Maybe it's gain is excessive or set too high if it has an input level control. I didn't see any mention of what associated equipment you are using.

 

[NoTransistors]

It is driving a Van Alstine MOSFET amp that was built on a Dynaco Stereo 70 chassis .
All parts except the transformer are Van Alstine. Amplifier has no potentiometers except for transistor bias.
What I have just done to the preamp was to series a 200 ohm resistor to each factory value turntable gain setting resistor.
This has improved the over-amplified noises associated with cranking the volume on a phono setup, without lowering the stylus onto a record. It also revealed a bit of noise on one phono board. Rebuilding them is very cheap.
But why the excessive gain? Seems to be from the board with the final-gain stage and tone control, as any input is too loud.

Associated equipment includes:
Dual 1219
Sure ML140HE
Stacked Pioneer CS-99A and Heil Driver

Gain is more normal with a Van Alstine pre-amp that I own and do not like.