amp builders or diy guys ?

[seti]

Eric thank you for your input. I took so better pic of the area in question.

I asked for really nice speaker binding post on the rebuild and this is what I got.

I'm getting good with this camera on macro setting. Here is the money shot.

A little fuzy.

Sorry for the large image size links but I didn't want to loose detail shrinking them.

[seti]

This is the fuse plug that broke off in shipping and was resoldered.

[Erik Mandaville]

Okay, thanks for confirming the connection point of that one wire. It's connected to the ground point of the input jack, which is not insulated from the chassis -- which means that the amp *may* not have a single chassis ground point (aka Star Ground). Studying the pictures, I think I see a couple of other connection points that are grounded to the chassis. Using the input ground point for the chassis star ground connection is common, but it doesn't *appear* to be the only part of the circuit that's grounded to the chassis; and that can sometimes cause problems (hum).

I see that some of the older capacitors have been replaced, however the original .33uf tubular and 50uf electrolyitic bypass caps in that first stage have not been. That's not necessarily a bad thing, but I would like to see modern counterparts of those used. Capacitors (and resistors) can drift in value after so many years, become leaky, and so forth. There could be other areas worth studying, but that entire first stage seems to me to be worth looking at more closely.

Erik

[Erik Mandaville]

I also see a ground buss wire (near where you can see 110V 120V printed on the chassis). That's an important ground collection point for the power supply, and that *seems* to be run over to the RCA jack ground. That would be expected, but it's the one or two other ground points that could be a problem if I'm interpreting the pictures right.

The common (ground) connection on the speaker output binding post is also ambiguous in terms of associated connections I see on the output transformer secondary. What else was done to this amp? Are you using it as a monoblock?

Also: Are the volume controls operational? Have you been going straight from your souce into the amp?

[seti]

I also see a ground buss wire (near where you can see 110V 120V printed on the chassis).  That's an important ground collection point for the power supply, and that *seems* to be run over to the RCA jack ground.  That would be expected, but it's the one or two other ground points that could be a problem if I'm interpreting the pictures right.

The common (ground) connection on the speaker output binding post is also ambiguous in terms of associated connections I see on the output transformer secondary.  What else was done to this amp?  Are you using it as a monoblock? 

Also:  Are the volume controls operational?  Have you been going straight from your souce into the amp?

I obviously need a dummies guide to electronics as applied to tube amps.

The guy that rebuilt this unit said it sounded wonderful when he was finished with it but when I got it the amp back it was a mess. The amp was not anchored in the wooded crate like I sent it so it came back brokern  loose busting the speaker binding post and fuse plug was obliterated. I originally sent two of these but only got this one back after a year. The transformers from the second he said were bad but after the run around/lies I asked for them back and finally did but never have received the chasis. The tubes I sent with the amp were NOS from Brent Jessie and the rebuilder so poorly packed them that most of the tubes were broken when I got them back. It is sad to see four JAN RCA 5AR4 tubes wasted like that. I sent all tubes double wrapped in bubble wrap but all he did was put a bit of foam over them. Also I requested that all caps and resistors be replaced which they were not. The guy said he woudl put a pentode to triode swich on the amps as well but never did. I was so mad about the state of this project that I have been sitting on the amps and parts for a while. Then last week I see another of these on ebay AS-IS so I snagged it for $150 now I have another and if it is good I'll be happy. Believe it or not this isn't even half the story LOL...

The volume control on the monoblock is operational. Yes I was running it just with CDP to amp to Belle but cheap speakers the first time. I was planning on using these with my Belles. The thought of 65-90 watt monoblock tube amps with tube voltage regulation seemed really cool. They look like a regular light show with all 9 tubes lit up. I have one that barely works and another in need of tlc. I just pray the transformers are OK.

I am sending these to some guys I have been talking to in Mississippi which I like because if something goes wrong I can drive three hours to pick up my equipment. They are very knowledgable and have set time frames for evaluation, quote, work to be completed, and amp burned in. They say they rarely have gear for more than a month or two. 

The moral of this story is be very very very careful who you send your gear to be worked on too.

[seti]

I think you might be on to something as I was doing my annual search for things related to this amp and found this guys post.

I just did another "test toast" (I LOVE that term!) running my Allen 90 that was damaged in shipping. Not only was it damaged, but it had some technical issues because someone who modified it made mistakes. Thank goodness I was able to locate a schematic online, complete with ref. voltages.

It seems that someone replaced all the capacitors, but also created several ground faults by making ground connections to the chassis at the input jacks and throughout the high voltage supply (a no-no learned in hi-fi amp 101). there was also a mis-connection in the high voltage supply to one of the signal tubes. Once I corrected these errors, the sound came into focus like a mountain panorama does to a man wearing glasses for the first time.

Unannouced to this journal, I've also picked up a SECOND Allen model 90 (in much, much better shape though be it also damaged during shipping to me). This has proven quite help\ful in de-bugging the more problematic one.

I was planning on using a solo allen 90 to drive the subwoofer in my monster surround sound system, but now that I have two, I might use them as left and right front, and get another Allen 90 for the sub, or something different. (maybe *gasp* solid state!)

I guess I could go whole hog and run two Allen 90' in the sub. That seems like a bit of a waste, though.

The '90 uses two glow-discharge voltage regulator tubes in the power supply. They sop up extra current from the high voltage supply, and the light they give off will actually pulse with the beat, as power is taken from the B+ reservoir and pushed through the tubes.

I can't stand it any longer. Here is a picture for your viewing pleasure. (um, tough shot. you ge a low-res. sorry)

Here is a pic of those 0D3 tubes.

It seems these amps could be cursed for shipping and techs LOL.

[Erik Mandaville]

Those mercury vapor regulators are neat looking, but I have heard on occasion over the years where some have reported noise in association with them. That may have nothing to do with the problems you're having, but just thought I would mention it.

I agree with those comments concerning grounding, which is something that has to be dealt with constantly.

I've done about the best I can to try to help from pictures, but it obviously doesn't repair the amp for you. I can understand your interest in these big old things, though. I once had a Baldwin organ amp that was incredible.

I hope things work out better with the next one!

Erik

[Erik Mandaville]

One of my most special tube "devices' uses a regulator like that. I'll take a picture of it if you'd like to see another component that uses a similar regulator. This is an entirely hand-built regenerative receiving radio, and is an absolute lesson in workmanship and point-to-point wiring. Among the very best I have ever seen, including audio amplifiers.

Erik

[mike stehr]

"The moral of this story is be very very very careful who you send your gear to be worked on too."

That's why I chose to DIY. I can only be mad at myself for desecating a circuit. And I'm not out any cash....

If you are concerned over if the transformers are any good on the Allen 90's you just purchased, buy a cheap DMM at harbor freight and check resistance in all the leads of the PS x-former, chokes, and the output transformers. You may have to lift a couple leads.

Check DC resistance for shorts, or open windings. A open winding will give no reading.

Check the DCR for the power supply transformer primary, secondary, and heater windings. Measure resistance on another mono 90 PS transformer's windings and see if the match up with the first measured PS transformer windings. They won't be exact, but should be relatively close. If one is way off, then something's wrong.

The chokes you just check for a open winding, and you'll know the DCR.

Are you sure the Allen 90's you have use a 5AR4? The schematic shows 5R4. Which I'm pretty sure is a directly heated rectifier, and the diagram shows no cathodes on the rectifiers. I'd rather hunt for 5R4's than 5AR4's.

I would think the Allen 90 uses more than one chassis ground, I dunno...

One rule of thumb I've been shown, is to make sure first power supply capacitor's ground lead/lug/terminal is grounded with the power supply transformer's center tap.

But this is a choke input supply with the power tapped off the 5 volt heater winding center tap, so I don't know if the rule applies here.

[seti]

One of my most special tube "devices' uses a regulator like that.  I'll take a picture of it if you'd like to see another component that uses a similar regulator.  This is an entirely hand-built regenerative receiving radio, and is an absolute lesson in workmanship and point-to-point wiring.  Among the very best I have ever seen, including audio amplifiers.

Erik

 

 

Thank you so much for taking the time to look at least I have a few leads. I'd love to see a pick of another regulator tube. I think they use something like this in one of the bottleheaf preamps.

[seti]

"The moral of this story is be very very very careful who you send your gear to be worked on too."

 

That's why I chose to DIY. I can only be mad at myself for desecating a circuit. And I'm not out any cash....

 

If you are concerned over if the transformers are any good on the Allen 90's you just purchased, buy a cheap DMM at harbor freight and check resistance in all the leads of the PS x-former, chokes, and the output transformers. You may have to lift a couple leads.

 

Check DC resistance for shorts, or open windings. A open winding will give no reading.

Check the DCR for the power supply transformer primary, secondary, and heater windings. Measure resistance on another mono 90 PS transformer's windings and see if the match up with the first measured PS transformer windings. They won't be exact, but should be relatively close. If one is way off, then something's wrong.

 

The chokes you just check for a open winding, and you'll know the DCR.

 

Are you sure the Allen 90's you have use a 5AR4? The schematic shows 5R4. Which I'm pretty sure is a directly heated rectifier, and the diagram shows no cathodes on the rectifiers. I'd rather hunt for 5R4's than 5AR4's.

 

I would think the Allen 90 uses more than one chassis ground, I dunno...

One rule of thumb I've been shown, is to make sure first power supply capacitor's ground lead/lug/terminal is grounded with the power supply transformer's center tap.

But this is a choke input supply with the power tapped off the 5 volt heater winding center tap, so I don't know if the rule applies here. 

I always get the 5ar4 confused with 5r4 which is what I have sorry. Wish I had the knowledge of this stuff you guys do sheesh. Think I'll send off both amplifiers and the additional transformers for them to check out. Do you guys have any suggested reading for newbies? I have always wanted to try a bottlehead preamp kit.

[mike stehr]

http://www.tpub.com/content/neets/14178/css/14178_13.htm

[Erik Mandaville]

Of course -- no problem at all. I have a couple of books that might be helpful.

I'll post a picture of that component tomorrow.

Erik

[Erland]

Maybe I am just picky when it comes to electronics, but I did not think what I saw on your picture, look like something that's made by a pro repair or a manufactorer! It looks more like the first DIY project that I did some years back (that I took apart and remade at a later stage due to the mess,humm ea.

From the picture I can not point out anything in particular that seem wrong, but it looks like at least two leads parts from another, for then to go back together again (with not component between, and for no particular reason). Is that so? If yes, in theory it should not matter, but in reality it does! I have experienced that such things sometimes things like that creates kind of an anthenna-effect, or the litle "loop" causes humm. As said, hard to tell from a pic.
In my opinion and excperience, NO internal components should touch each other.

I have been stugling with humm at different occations, and it's rearly easy. The most difficoult is when the humm is related to the ground that due to the design of the different components (source/pre/power) comes at different levels (i do not know how to explain this one better). I have experienced that to run the preamp "hardground" and the rest of the compoents floating, makes the most stable and silent system for me.

I can not tell what's wrong or right, and what I have written above, is definately not textbook electroics. I just like to forward whats been working in my system.

[seti]

Maybe I am just picky when it comes to electronics, but I did not think what I saw on your picture, look like something that's made by a pro repair or a manufactorer!  It looks more like the first DIY project that I did some years back (that I took apart and remade at a later stage due to the mess,humm ea.

From the picture I can not point out anything in particular that seem wrong, but it looks like at least two leads parts from another, for then to go back together again (with not component between, and for no particular reason).  Is that so?  If yes, in theory it should not matter, but in reality it does!  I have experienced that such things sometimes things like that creates kind of an anthenna-effect, or the litle "loop" causes humm.  As said, hard to tell from a pic.

In my opinion and excperience, NO internal components should touch each other. 

I have been stugling with humm at different occations, and it's rearly easy.  The most difficoult is when the humm is related to the ground that due to the design of the different components (source/pre/power) comes at different levels (i do not know how to explain this one better).  I have experienced that to run the preamp "hardground" and the rest of the compoents floating, makes the most stable and silent system for me.    

I can not tell what's wrong or right, and what I have written above, is definately not textbook electroics.  I just like to forward whats been working in my system.

 

I have shown these pics to many people and so far the responses have been the same. When I send off the amps and transformers I will request them to tidy up and examine/rework the grounding. I am still having trouble identifying the transformers.

Thanks!

[Erland]

Literature:

Morgan Jones - Valve Amplifiers

Well written - most be the closest thing to "Tube amps for dummies"

[scout233]

Hi,

Although I am late getting into this conversation, I wanted to add a little info/experience. I too was a newbie to tubes some years back when I attempted to resurrect a integrated tube amp my dad bought while in viet nam. Well, I too sent the amp off to a technician near san diego, i believe. When the amp was returned, it was packed poorly and the power cord was cut by the weight of the amp chasis. Needless to say, it was a great disappointment.

Later, I was lucky to find Paul Grzybek from www.2baudio.com . I drove the amp to his place and he immediately fixed many problems on the power supply side of the amp. And this was on an old Sansui amp.. that makes the under side of your amp look sparse! He has had countless vintage tube amps apart and restored them. Currently, he has been working on his own line of tube amps, but i believe he still does repairs/restorations on the side. Also, he is a genuinely nice guy that takes incredible pride in his work.

Hope this info may help someone that feels there is no place to turn with their old cherished tube amps.

Dave

[seti]

I have posted on several forums about these amps. The advice and comments I have received has led me to get out while I can. This was suposed to be a couple month project that has gone on way too long and taken up too much money. I will ebay the entire lot of monoblocks, transformers, and tubes all in one auction. If I can recoup a fraction of the cost I'll be happy. Hope to have the auction posted today.

1 monoblock rebuilt reportedly sounded good but damaged in shipping resulting in humm.

1 monoblock needs to be restored like the first one but without hum...

1 Extra set of transformers that need to be tested may or may not work. I just don't know.

3 JAN RCA made brown base 5R4 NOS from Brent Jessie

3 6550 Valve Art Polished Base Tubes New

2 6550 Tung-Sol grey smoothe grey plate 1960's US made not tested

1 KT88 Genalex it looks like hell but tests good

6 0D3 GE RCA with GE Carton

1 Sylvania 12AU7

blocks

perhaps the proceeds will go to a floor sander LOL

tubes

Hopefully they will sell fast. Shipping will be pricey so I hope to keep the price reasonable. New pics of tubes and blocks for auction. I posted comments to go with most of the pics.

Buh Bye

[seti]

Excellent my brother offered me $475 for the entire lot and I don't have to ship anything! Now to find a new project perhaps some of them speakers that fir into a corner.

[drewski_brewski]

Lol, hi, this is Drewski_Brewski, and I found your post of my post while searching for articles relating to the Allen Type 90, so I joined the group! (I'm very excited to find others discussing this) The original input jacks on these amplifiers are an old-style threaded coaxial Amphenol connector, and it is completely insulated from the surrounding chassis. If a person converts over to RCA, they must isolate the RCA jacks and return the ground in the same manner as the original circuit. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

A note about the amp I own above: From day one, the B+ was much higher than the schematic indicated it should be, and I checked and double-checked the circuit, capacitors, resistors, choke, etc, until I finally measured the open-circuit voltage of the AC transformer, and found it to be about 250 volts higher than my other Allen 90's. Then, I looked at the notes on the schematic, and noticed that the serial numbers for the Type 90 start at 5000, and I own number 5005! Several of the components differ from the other '90's that I own and I suspect this one was built using substitute parts before Allen got their supply chain in full swing. I could be wrong, but it's a great theory.

I didn't scrutinize this string... did the subject amp ever get fixed?