Recapping a preamp

[rrcrain]

Any thoughts or experience replacing old capacitors in preamps? Specifically, I've a 20+ year old Heathkit AP-1800 that contains 47 electrolytics along with a collection of ceramic, mylar, tantalum and polystyrene. I'm thinking the only ones that may be problematic are the electrolytics.

[dynaco_dan]

Hi Richard

I am not familiar with this particular pre-amp but here goes my opinion.

The electrolytics usually leak and with 47 potential to replace I am going to make another suggestion if you don't mind.

If this was an Audio Research or equal quality then maybe you might attempt to replace the electrolytics, etc..

You would buy 105' computer grade caps and your are looking at over $100.00 plus, plus. Check out Mouser.com or others re prices.

If this doesn't deter you, then good luck.

Another alternative might be to buy a Dynaco Pat 4 or Pat 5 or Pat 5 Bi-Fet for maybe $50.00 from eBay.

There is other brands, but for a minimal outlay, this is what I would suggest you give thought to, as money well spent.

Good luck, Richard.

Vern

>Any thoughts or experience replacing old capacitors in

>preamps? Specifically, I've a 20+ year old Heathkit AP-1800

>that contains 47 electrolytics along with a collection of

>ceramic, mylar, tantalum and polystyrene. I'm thinking the

>only ones that may be problematic are the electrolytics.

[rrcrain]

In 1982, this preamp ran $450 in kit form. I'm not familiar with the Dynaco to know if it's an equivelant or better design than what I have, but I do know that Heathkit didn't make many compromises in their Pro Series of stereo equipment.

[dynaco_dan]

Hi again

I don't know if there is a Heathkit web site out there, but that might be a better source of comparing the quality of your pre-amp to what is available new or used today.

I didn't mention anything new today because prices have kinda gotten out of control, thousands of dollars.

One only has to read Stereophile to see what I mean.

The price of your pre-amp was high and I assume it was a quality pre-amp back then.

I assembled Heathkits and Dynakits and Heath definitely gave you more quality in circuit boards and manuals than Dynaco in my opinion.

"Dynaco, gave more bang for the buck," in almost all cases, but the inside component quality, circuit boards and manuals were at a lower level than Heath in my opinion.

You paid for what you received and because Dynaco was lower priced and distributed more openly and consumer acceptance was extremely high, sales were wild.

Almost every review in a magazine was very favourable and each product was priced so much lower than those currently available.

I presently own several Dynaco pieces and my brother used to own several Heathkit pieces. AJ-15, AA-15 and AR-1500 receiver if I remember correctly. These were top of the line in hifi at that time. Well reviewed, as I remeber, as well.

Allowing for your own careful skills and patience a Heathkit project looked real fine when completed and gave a greater feeling of acccomplishment, in my opinion.

A Dynaco tube PAS-3x which may have been $100.00 in 1970 +/- in kit form, is now, because of collectablity, selling for several hundred dollars or more.

A Dynaco solid state Pat-4 may have sold for $100.00 in 1970 and now can at times be bought for $35.00 depending on if it was modified and general condition.

Have a great day.

Vern

>In 1982, this preamp ran $450 in kit form. I'm not familiar

>with the Dynaco to know if it's an equivelant or better design

>than what I have, but I do know that Heathkit didn't make many

>compromises in their Pro Series of stereo equipment.

[Guest Bret]

>I presently own several Dynaco pieces and my brother used to own several Heathkit pieces. AJ-15, AA-15 and AR-1500 receiver if I remember correctly<

One of those wouldn't happen to be a MK II with the MK III transformer upgrade on it, would it? That upgrage was ugly because the basket would never fit again, but evidently a lot of people did that when the MK III was proclaimed to be so much superior to the MK II.

But that amp used to power a Janszen dual-panel electrostatic cabinet sitting atop an AR-1W. How did it sound? Like 1/8" thick 1954 monaural recordings being spun on a 100 lb Rec-O-Cut!

Bret

[dynaco_dan]

Hi Bret

Other than a SCA-35 that I owned back in the late sixties, I only have FM-3's that are tube.

What I have read though, and this is way back, the Stereo 70 with a PAS-3X or 2 - Mark 111's was really a very high standard of THAT day.

In my Dyna hifi museum, I have, FM-3's, SCA-80 & Q, Stereo 120, Pat-4, Pat-5, Pat-5-Bi-Fet, Stereo 410, Stereo 400, Stereo 400 Double Dyna, FM-5 and AF-6.

The Janszen's were sold individually, the same as any other speakers, you only needed a pair laying horizontally on a horizontal AR-1, AR-1w AR-3 or AR-3a.

The enclosure had 4 electrostaic panels in an enclosure the same shape as the Microstatics which also had 4 tweeters, 2 different sizes.

The AR-1W, Janszen 130 electrostaic speaker system and The Microstatic speaker sysem was "Consumer Guides" ( Not Consumer Reports ) reference system way back.

You would only use the woofer section.

I had an opportunity to have a pair on loan, as well as, Microstatic tweeter array.

I believe the AR-3A was a better match because of the lower crossover of the woofer over to the Janszens.

With this setup and using only an AR amplifier at the time, it sounded really wonderful.

I still remember playing, "Cecelia," with Simon and Garfunkle and everyone listening was really impressed and drooling.

The Janszen drivers were later used as well in the KLH Nines.

Have a great day again.

Vern

>>I presently own several Dynaco pieces and my brother used to

>own several Heathkit pieces. AJ-15, AA-15 and AR-1500 receiver

>if I remember correctly<

>

>One of those wouldn't happen to be a MK II with the MK III

>transformer upgrade on it, would it? That upgrage was ugly

>because the basket would never fit again, but evidently a lot

>of people did that when the MK III was proclaimed to be so

>much superior to the MK II.

>

>But that amp used to power a Janszen dual-panel electrostatic

>cabinet sitting atop an AR-1W. How did it sound? Like 1/8"

>thick 1954 monaural recordings being spun on a 100 lb

>Rec-O-Cut!

>

>Bret

[dynaco_dan]

Hi again Bret

>

>I had an opportunity to have a pair on loan, as well as,

>Microstatic tweeter array.

>

>I believe the AR-3A was a better match because of the lower

>crossover of the woofer over to the Janszens.

>

>With this setup and using only an AR amplifier at the time, it

>sounded really wonderful.

>

>I still remember playing, "Cecelia," with Simon and Garfunkle

>and everyone listening was really impressed and drooling.

>

What I didn't mention was how, after listening to the AR-3A woofer, Janszen 130's and Microstatic's setup and then going back to just the AR-3A's alone was so dramatic.

What happened to the tweeters!

There gone or blown!

We are not talking of a subtle change, we are talking, major change.

Un-fortunately, the AR-3A's were about $375.00 cdn each, the Janszen's maybe $300.00 cdn/pair and the Microstatics for about $175.00 cdn/pair.

I do believe the AR-3A was a better match with the lower crossover and had less interference with the Janszen's than would a AR-3, AR-1W, AR-1, or AR-1X unless a lower crossover was created.

Just thinking about it now, tri-amping might have been another idea.

At that time it was a lot of money, I never did own other than the 3A's.

I had a WAF ( Wife Acceptance Factor ) of zero at that time.

Looking back, I wish, I had Tom's strong will and just bought them and took my punishment.

Being in the doghouse and sleeping on the couch isn't that bad after all.

Have a great evening.

[rickrob2]

The Dynaco PAT-4 would be a good preamp- I would recommend that you do the Van Alstine mods to it. The Bi-Fet PAT-5's go upwards of $100 or more on EBay and the PAT-5 are around $80-$90, and either would probably need some re-cap work just due to age if anything. A decent PAT-4 can be purchased for about $40-$50. and the parts to do Van Alstine's mods for another $40. With the mods, the PAT-4 is a pretty good preamp.

[dynaco_dan]

Hi again Richard

If you still are thinking of replacing the caps in the Heath, you also may wish to replace all of the resistors with metal film as well as, all of the electrolytic caps.

Replacing all diodes and zeners in the power supply might also be advantageous.

Good luck and please keep us updated as to your progress.

[rrcrain]

I've made a list of the electrolytics (about 50) and will spend some time researching prices and types before I make a decision.

Since I'm the builder of this unit, I've a bit of faith the resistors and diodes weren't stressed during assembly. Truth be known, this unit has performed without failure its entire life. It is beginning to have an odd problem with channel balance that comes and goes, and I'll probably send it in for service at some point in the near future.

Interestingly, the preamp lacks zeners, though it does have two heavily filtered full wave rectifiers. One for the unit, the other for the M.C. section.

[dynaco_dan]

Hi again Richard

When I suggested replacing the resistors it is because they may be carbon composition rather than carbon or metal film.

They change in value with usuage and heat, also they may have been 10% - 20% tolerance as well.

Back then, there was a small price difference, but still in quantity there was a savings to manufacturers.

Also today 1% values are more readily available.

They usually can be bought in strips of 10 or so.

You can, if you have a digital meter, even try to mate each pair per channel.

The diodes do deteriorate with usuage and there again the tolerances may be tighter today.

The caps should be computer grade 105'C rated not the cheaper 85'C.

Panasonic has a good reputation for these caps.

Often there is a qty price breaks such as 1-9 $1.00 ea then 10-25 $.65 ea. It pays to shop and even if you have a few spares it's ok.

Just for your information if 100uf - 25v elect cap is called for 150uf - 50v is acceptable in most cases. Space determines size.

If any resistors looked overheated or the boards are scorched use a larger wattage rating. Generally 2 watt is a high wattage resistor.

There was 5 watt carbon compositions used and by paralleling 4 - 2 watt resistors this problem can be overcome.

Overall you won't need to change all of the parts in the pre-amp but the ones I've suggested will improve the sound ( quieter ) and longterm reliability.

De-oxit on switch contacts will ensure reliablity of the contacts.

A stock Pat-4 was not the absolute best of pre-amps when I suggested it, but is an, " absolute best buy" with simplicity, at a price of around $40 - $50 on ebay for the stock unit.

I am assuming the switches function correctly as they are generally not available on the parts market, they were specially manufactured OEM for Dynaco.

The Audio Amateur had oodles of mods for the Pat-4 as well as for the Pat-5 pre-amps.

This is not the way to go in my opinion, you end up throwing almost everything away and using the chassis only and now having to re-create another pre-amp.

If you have nothing else to do and lots of money by all means go ahead.

You would end up with a slightly more superior pre-amp than stock.

I have the Audio Amateur issues and my next posting I'll try too look up how many references there is for both pre-amps.

There is a lot.

Good luck again, Richard.

>I've made a list of the electrolytics (about 50) and will

>spend some time researching prices and types before I make a

>decision.

>

>Since I'm the builder of this unit, I've a bit of faith the

>resistors and diodes weren't stressed during assembly. Truth

>be known, this unit has performed without failure its entire

>life. It is beginning to have an odd problem with channel

>balance that comes and goes, and I'll probably send it in for

>service at some point in the near future.

>

>Interestingly, the preamp lacks zeners, though it does have

>two heavily filtered full wave rectifiers. One for the unit,

>the other for the M.C. section.

[dynaco_dan]

Hi again Richard

Sometimes I can't stop what I'm doing, so here is the Pat-4 count and Pat-5 and Bi-Fet count;

The Audio Amateur reference or comments only on the following.

I have not separated actual mods from comments in my counting.

Pat-4 pre-amp 47 references or comments

Pat-5 pre-amp & Bi-Fet version 154 references or comments

There is a lot of data to be sure.

The Pat-5 BI-Fet has a number of features over the Pat-4, again at a price increase.

I would caution you and anyone else who buys a Dynaco Pat-5-Bi-Fet pre-amp that was wired as a kit the normal power switch doesn't turn on the pre-amp.

It is on all the time to maintain constant temperature and to eliminate the turn on transient and send it to the to the amp.

The excellent Dynaco owners manual offers an alternative solution for those who wish to alter this setup.

I mention this in case a power bar is being used.

The turning on of the power bar would send the startup transient to the amp which is just starting up and whap, maybe a speaker or two bites the dust.

Again good luck, Richard.

>

>When I suggested replacing the resistors it is because they

>may be carbon composition rather than carbon or metal film.

>

>They change in value with usuage and heat, also they may have

>been 10% - 20% tolerance as well.

>

>Back then, there was a small price difference, but still in

>quantity there was a savings to manufacturers.

>

>Also today 1% values are more readily available.

>

>They usually can be bought in strips of 10 or so.

>

>You can, if you have a digital meter, even try to mate each

>pair per channel.

>

>The diodes do deteriorate with usuage and there again the

>tolerances may be tighter today.

>

>The caps should be computer grade 105'C rated not the cheaper

>85'C.

>

>Panasonic has a good reputation for these caps.

>

>Often there is a qty price breaks such as 1-9 $1.00 ea then

>10-25 $.65 ea. It pays to shop and even if you have a few

>spares it's ok.

>

>Just for your information if 100uf - 25v elect cap is called

>for 150uf - 50v is acceptable in most cases. Space determines

>size.

>

>If any resistors looked overheated or the boards are scorched

>use a larger wattage rating. Generally 2 watt is a high

>wattage resistor.

>

>There was 5 watt carbon compositions used and by paralleling 4

>- 2 watt resistors this problem can be overcome.

>

>Overall you won't need to change all of the parts in the

>pre-amp but the ones I've suggested will improve the sound (

>quieter ) and longterm reliability.

>

>De-oxit on switch contacts will ensure reliablity of the

>contacts.

>

>A stock Pat-4 was not the absolute best of pre-amps when I

>suggested it, but is an, " absolute best buy" with simplicity,

>at a price of around $40 - $50 on ebay for the stock unit.

>

>I am assuming the switches function correctly as they are

>generally not available on the parts market, they were

>specially manufactured OEM for Dynaco.

>

>The Audio Amateur had oodles of mods for the Pat-4 as well as

>for the Pat-5 pre-amps.

>

>This is not the way to go in my opinion, you end up throwing

>almost everything away and using the chassis only and now

>having to re-create another pre-amp.

>

>If you have nothing else to do and lots of money by all means

>go ahead.

>

>You would end up with a slightly more superior pre-amp than

>stock.

>

>I have the Audio Amateur issues and my next posting I'll try

>too look up how many references there is for both pre-amps.

>

>There is a lot.

>

>Good luck again, Richard.

>

>

>

>

>>I've made a list of the electrolytics (about 50) and will

>>spend some time researching prices and types before I make a

>>decision.

>>

>>Since I'm the builder of this unit, I've a bit of faith the

>>resistors and diodes weren't stressed during assembly. Truth

>>be known, this unit has performed without failure its entire

>>life. It is beginning to have an odd problem with channel

>>balance that comes and goes, and I'll probably send it in

>for

>>service at some point in the near future.

>>

>>Interestingly, the preamp lacks zeners, though it does have

>>two heavily filtered full wave rectifiers. One for the unit,

>>the other for the M.C. section.

>

[rrcrain]

Very few of the original resistors were carbon, and fewer yet were less than 5%. I've had the power supply board out and did an extremely close inspection of it and theres absolutely no signs of overheating or stress anywhere in the unit. A fast review of the assembly manual shows a total of 5 10% resistors, the remainder being either 5% or 1%. Off the top of my head, there are 8 diodes in the unit.

No heat related stress on any component, on any board nor obvious signs of corrosion. The switches have been treated with Deoxit and Pro Gold.

One concern I have is the wiring. A couple of years ago, I ripped out the 75ohm coax in the power amp and found it to be severely corroded, to the point the wire was a major hinderance to performance. (It had turned black with hints of green) The pre amp is slightly older than the amp, and contains far more coax than the amp does but a different type. The amp has perhaps 24 inches of copper wire braid coax whereas they used aluminum foil wrapped coax in the pre amp. (Yes, I can hear the wire fanatics rolling over in their graves.) I'm super reluctant to replace wire for the sake of wire type as I view it as a minimalistic improvement if that.

[dynaco_dan]

Hi Richard

I wouldn't replace any wires unless the insulation has deteriorated and crumbled, which might create a short circuit.

The green is patene, copper oxide, from soldering paste and copper wire.

If you didn't use acid core solder to assemble it with, and Heath wouldn't have supplied any, not to worry.

All of the smaller resistors should be carbon type, but whether they are composition type or deposit type is the issue.

If they are composition and in the signal path then you would want to upgrade to film type at 1% tolerance, while you are upgrading to new caps.

I am talking of a few pennies each at most and a little soldering.

I know that there is high end resistors, but I'm not going there.

There is also high end caps, but I'm not going there either.

Unless the diodes are very special, hard to obtain values, I would replace them also.

All of the parts you replace will provide, if you measure each parts value, a measure of balance, which no normal manufacturer can afford to do, to the best available.

In the power supply, which probably only draws a few watts, stability is all that's important here.

If you are soldering, I recommend, silver - tin - lead 2% - 10% - 88% as a readily available electronics supply house solder, rosin core flux or equiv..

A temperature controlled soldering iron such as Weller WCPT.

Patience and care in doing the job, and the results will be there.

Good luck again.

>Very few of the original resistors were carbon, and fewer yet

>were less than 5%. I've had the power supply board out and did

>an extremely close inspection of it and theres absolutely no

>signs of overheating or stress anywhere in the unit. A fast

>review of the assembly manual shows a total of 5 10%

>resistors, the remainder being either 5% or 1%. Off the top of

>my head, there are 8 diodes in the unit.

>

>No heat related stress on any component, on any board nor

>obvious signs of corrosion. The switches have been treated

>with Deoxit and Pro Gold.

>

>One concern I have is the wiring. A couple of years ago, I

>ripped out the 75ohm coax in the power amp and found it to be

>severely corroded, to the point the wire was a major

>hinderance to performance. (It had turned black with hints of

>green) The pre amp is slightly older than the amp, and

>contains far more coax than the amp does but a different type.

>The amp has perhaps 24 inches of copper wire braid coax

>whereas they used aluminum foil wrapped coax in the pre amp.

>(Yes, I can hear the wire fanatics rolling over in their

>graves.) I'm super reluctant to replace wire for the sake of

>wire type as I view it as a minimalistic improvement if that.

[rrcrain]

The wire I was referring to in the amp had turned black to dark green the entire length of the coax. Only thing I can think of is it was either bad coax from the start or it didn't like sailing around the Atlantic and Med for over half a year back in the 80's. (AA-1800)

I agree and disagree on the solder type. Atinic(sp?) solder melts at a significantly lower temperature than either the 2% silver or standard silver, and is therefor generally preferred for solid state for this reason. I recently completed a Marchand tube crossover and used the atinic for this very reason. On the other hand, the 2% silver may provide a slightly more conductive joint.

There could be a lot more done if one was of the mind. One could argue that the transistors comprising the op-amps have weakened with age and should be replaced or that the silver mica caps need replacing due to whatever. But for now, I'll limit the project to the electrolytics and perhaps the rectifier diodes. The resistors aren't carbon so I'm not going to worry about this time around.

The resistors in the power amp are carbon, and have a history of failing in this amp. They do need replacing.

[dynaco_dan]

Hi again

You don't sound happy that I'm suggesting more than just the caps?

You brought up the transistors now, and maybe there is an improved version available, like for like.

>The wire I was referring to in the amp had turned black to

>dark green the entire length of the coax. Only thing I can

>think of is it was either bad coax from the start or it didn't

>like sailing around the Atlantic and Med for over half a year

>back in the 80's. (AA-1800)

>

>I agree and disagree on the solder type. Atinic(sp?) solder

>melts at a significantly lower temperature than either the 2%

>silver or standard silver, and is therefor generally preferred

>for solid state for this reason. I recently completed a

>Marchand tube crossover and used the atinic for this very

>reason. On the other hand, the 2% silver may provide a

>slightly more conductive joint.

>

>There could be a lot more done if one was of the mind. One

>could argue that the transistors comprising the op-amps have

>weakened with age and should be replaced or that the silver

>mica caps need replacing due to whatever. But for now, I'll

>limit the project to the electrolytics and perhaps the

>rectifier diodes. The resistors aren't carbon so I'm not going

>to worry about this time around.

>

>The resistors in the power amp are carbon, and have a history

>of failing in this amp. They do need replacing.

>

>

[rrcrain]

>>You don't sound happy that I'm suggesting more than just the caps?

Not at all. I'm more of the opinion that there is a real point of diminishing return.

>>You brought up the transistors now, and maybe there is an improved >>version available, like for like.

Perhaps, but I've some doubts. It's equally possible that some of the transistors are obsolete, and to replace them would require a fair amount of circuit modifications.

Since I've been away from the bench for over 14 years, I no longer have or have access to the reference books or test equipment I once did.

[Guest daveshel]

>The Dynaco PAT-4 would be a good preamp- I would recommend

>that you do the Van Alstine mods to it. The Bi-Fet PAT-5's go

>upwards of $100 or more on EBay and the PAT-5 are around

>$80-$90, and either would probably need some re-cap work just

>due to age if anything. A decent PAT-4 can be purchased for

>about $40-$50. and the parts to do Van Alstine's mods for

>another $40. With the mods, the PAT-4 is a pretty good

>preamp.

Do you have a link for how to do the van Alstine mod on the PAT-4?

[Guest slbender]

That Heathkit 1800 Preamp probably does need all the electrolytic caps replaced; my older Heathkit AR-15 AM/FM Stereo Receiver plays for about ten minutes before it loses one channel, so I probably should be replacing its zillions of electro cap's too, and probably some transistors and resistors. But frankly, that project is so intimidating, I'll just start off by getting my feet wet - repairing a few blown-up NAD Stereo Receivers, a few early Harman-Kardon's, and Fishers, and then onto the Gold faced AR Receivers, and AR Integrated Amps, and work my way up to the Heathkit AR-15, probably by around 2015... and then I'll also do the AA-15 and AJ-15 separates.

Well good luck and wishes for best results with your 1800 Preamp,

-Steven L. Bender

[rrcrain]

My preamp project has been put on hold due to several life events; Most notably moving. We decided to move out of the city to the country and have purchased a home sitting on 10 acres of timber and the house has the potential of being an incredibly nice home but for now, it's a project house. We have several "have to do" projects right up front and once they are completed, my darling wife has a plethora of "want to do" projects already lined up with more on the way. Thankfully, come spring, she will be to busy gardening to do anything else.

As far as warm up projects leading up to the preamp, I suspect building a Marchand tube crossover and rebuilding my AR90 crossovers was a decent warmup excercise.