1959 Hoffman Tube Stereo console...NOS...Amperex Tubes

kirk57 said:
The best tubes in the world aren’t going to help an amp with circuit or transformer shortcomings.

If the OP is going to repair the amp I’d suggest to replace all those Amperex tubes with something cheap, al least until the amp is known to be in good working condition. It *is* possible to ruin a tube by running it in a malfunctioning circuit.
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Good call, thanks! I’m gonna stick some old RCA 6BQ5’s, an old 12AT7, & Cheap 12AX7’s after any repairs :beerchug:
 
Hoffman amp.jpeg

Interesting EL84 tubes. rX3 = EL84 (3rd iteration). A8L = WIRAG Werke, Austria. Made Sept, prolly 1958.

I've never used or even seen an Austrian made Philips consortium tube before. :idea: :)
 
FlaCharlie said:
While the tuner may be the same, the OP's amp seems to be SE 6BQ5 while yours is PP.
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wasn't looking all that close, noticed the faceplate and what looked like the same tube lineup. Totally missed that its stereo SE where mine is mono push-pull on the same chassis. Mine is one of those early 2 piece stereo consoles, so I have two of those mono amps.
 
angelaudio said:
This is the resistor (circles in orange) that bubbled up, it’s underneath the can cap that got hot. View attachment 1846733
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That's what happens when you just plug something in that hasn't been used for decades. The can cap likely would have been fine (for now) with a soft start, but when you hit it with full voltage it overheats before it reforms. It also causes excessive current through the dropping resistor between sections. Any time you power something up for the first time, you need to frequently check the caps and power transformer to see if they are getting too hot.

The best way to to resurrect something like this is to either reform the electrolytics (ideally with a current limited DC power supply), or at least ramp the voltage up very slowly on a variac while monitoring current draw. If you can't do that, then you should replace the caps before even plugging it in.
 
Mr Boochie said:
View attachment 1847723

Interesting EL84 tubes. rX3 = EL84 (3rd iteration). A8L = WIRAG Werke, Austria. Made Sept, prolly 1958.

I've never used or even seen an Austrian made Philips consortium tube before. :idea: :)
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Thanks for that info Mr Boochie. I’m fairly new to tube gear so I must ask, are these tubes different/special because of their “made in Austria” stamp?
 
Mr Boochie said:
You're gonna have to tell us, after getting the unit up-to-snuff. I'm never heard an Austrian made EL84. :)
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Will do!

I’m looking for replacement can caps and I’m wondering if the following will be a suitable replacement:

Old can cap: 40mfd 350 W.V., 40mfd 350W.V., 50mfd 25WV, 50mfd 25WV

Replacement can cap for above: 50,50,50,50mfd 350

Would the replacement in question work or would I be ramping up the numbers too much for the 50mfd sections?
 
50/50/50/50 at 350 VDC, each? Will work fine. The 25WV ones are prolly bypass caps off certain tube cathodes. Extra voltage rating is fine, in those positions. :)

BTW... do you have the tuner section of this console unit?
 
a 20/20/20/20 with the sections strapped to make 40/40 and a pair of low voltage ones underneath would be a somewhat better fit. No need for more than 50v in that spot.
 
Mr Boochie said:
50/50/50/50 at 350 VDC, each? Will work fine. The 25WV ones are prolly bypass caps off certain tube cathodes. Extra voltage rating is fine, in those positions. :)

BTW... do you have the tuner section of this console unit?
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Cool. And yes I do indeed have the tuner as well, although I haven’t tried firing it up and won’t until I get some can caps for it too ;)
 
gadget73 said:
a 20/20/20/20 with the sections strapped to make 40/40 and a pair of low voltage ones underneath would be a somewhat better fit. No need for more than 50v in that spot.
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Shucks...I read your post too late. I had already ordered the aforementioned can cap with the higher voltage rating. If, as Me Boochie said, the 50mfd sections are indeed bypass caps off certain tube cathodes will I be running any type of risk by upping the voltage?
 
angelaudio said:
Shucks...I read your post too late. I had already ordered the aforementioned can cap with the higher voltage rating. If, as Me Boochie said, the 50mfd sections are indeed bypass caps off certain tube cathodes will I be running any type of risk by upping the voltage?
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Nope. Those sections are being used as bypass caps. Higher voltage rating for these sections will mean filtering may last longer.

Most cap cans run a tolerance range of (-10% to +30%) mfd or more. You'll be fine.

It's heat that kills cap cans (and most other 'lytics and non-polar types). Cans are usually rated to as low as 55-degrees C. Some as high as 85-degrees C. The higher rated ones will last longer under heated conditions, like tube amps.

Antique Electronics is a good source for electrolytic caps. They carry CE cap cans, which is newer iterations of the old Mallory types.

https://www.tubesandmore.com/products/capacitors?filters=Brand=CE Manufacturing

Be sure to mark those wires when removing or clipping them. Maintaining correct polarity and connections is super critical.

Good luck! Keep us informed. :thumbsup: :)
 
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angelaudio said:
I had already ordered the aforementioned can cap with the higher voltage rating. If, as Me Boochie said, the 50mfd sections are indeed bypass caps off certain tube cathodes will I be running any type of risk by upping the voltage?
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Too bad you already ordered cans. Individual caps are much, much cheaper and have better specs. For future reference . . .

Here's some comments I made about this in a post last year - different cap values since it related to a different amp but the general comparison is still valid:

I always suggest using caps rated at 105 degrees for 10,000 hours. Can caps are generally rated at only 85 degrees and sometimes less.

Replacing the cans is also a much more expensive option.

A CE can with four 20uf sections, sells for $36.70 plus shipping at Antique. Its heat rating is only 55 degrees, no hour rating listed and tolerance as much as +50%. Shipping costs for small orders can get expensive.

The cost of four individual Nichicons (22uf 450v) is $1.13 each for a total of $4.52. They are rated at 105 degrees for 10,000 hours and have a 20% tolerance. And, if ordered from Digi-Key, there's the free shipping option. Here's how you can get free shipping:

http://www.audiokarma.org/forums/in...hipping-on-parts-orders.739513/#post-10018562

So the CE can will likely cost about 10 times the price when shipping is factored in.

You can get custom made cans from someplace like Hayseed that use caps with the better specs but they are even more expensive than the CE cans. But, if limited space prevents you from using individual caps, the Hayseed caps are the way to go since the specs are better.
 
FlaCharlie said:
Too bad you already ordered cans. Individual caps are much, much cheaper and have better specs. For future reference . . .

Here's some comments I made about this in a post last year - different cap values since it related to a different amp but the general comparison is still valid:

I always suggest using caps rated at 105 degrees for 10,000 hours. Can caps are generally rated at only 85 degrees and sometimes less.

Replacing the cans is also a much more expensive option.

A CE can with four 20uf sections, sells for $36.70 plus shipping at Antique. Its heat rating is only 55 degrees, no hour rating listed and tolerance as much as +50%. Shipping costs for small orders can get expensive.

The cost of four individual Nichicons (22uf 450v) is $1.13 each for a total of $4.52. They are rated at 105 degrees for 10,000 hours and have a 20% tolerance. And, if ordered from Digi-Key, there's the free shipping option. Here's how you can get free shipping:

http://www.audiokarma.org/forums/in...hipping-on-parts-orders.739513/#post-10018562

So the CE can will likely cost about 10 times the price when shipping is factored in.

You can get custom made cans from someplace like Hayseed that use caps with the better specs but they are even more expensive than the CE cans. But, if limited space prevents you from using individual caps, the Hayseed caps are the way to go since the specs are better.
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I really don't know what cap can he ordered. I prolly would have gone with the 40/40/40/40 at 450VDC, if it fits. :idea: Higher voltage rating usually means more electrolytic solution in the can.

I have been using CE cans in my Champ and Vibro-Champ fixes and they are good cans. Even, with everyday use (which is prolly better for the can, anyways). Quality resistors between sections helps, too. I like wire wound ones (like 5-watt Mills) or 5-wattt metal oxide, for this reason. :)
 
Mr Boochie said:
I really don't know what cap can he ordered. I prolly would have gone with the 40/40/40/40 at 450VDC, if it fits. :idea: Higher voltage rating usually means more electrolytic solution in the can.

I have been using CE cans in my Champ and Vibro-Champ fixes and they are good cans. Even, with everyday use (which is prolly better for the can, anyways). Quality resistors between sections helps, too. I like wire wound ones (like 5-watt Mills) or 5-wattt metal oxide, for this reason. :)
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I went with a 50/50/50/50 350WV can cap from CE...it was pricey though at ~40 bucks shipped. Unfortunately this particular amp has almost no extra room underneath so it might have been nearly impossible to get any of the caps to fit underneath. For future repairs I’ll definitely try what @FlaCharlie suggested and go with individual caps underneath. I just got the can in last night so I’m somewhat tempted to just take it to the Doctor :D But if I did decide to operate on her myself would there be anything I would need to do in addition to just dropping the new cans in? For example...check any voltages, resistor values, bias etc? I have a very primitive grasp on reading schematics but I do have a DMM. Also thinkinung of picking up a Variac...they have a 500watt one for sale at my local electronics shop and I’m wondering if that would suffice:rolleyes:
 
angelaudio said:
I went with a 50/50/50/50 350WV can cap from CE...it was pricey though at ~40 bucks shipped. Unfortunately this particular amp has almost no extra room underneath so it might have been nearly impossible to get any of the caps to fit underneath. For future repairs I’ll definitely try what @FlaCharlie suggested and go with individual caps underneath.
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I understand that to someone who is just starting to explore the idea of refurbishing tube amps that it might look tight at first. Here's a pic from the Sams of the underside of the amp chassis. There is actually a LOT of space under there.
Hoffman Amp Bottom.png

angelaudio said:
I just got the can in last night so I’m somewhat tempted to just take it to the Doctor :D But if I did decide to operate on her myself would there be anything I would need to do in addition to just dropping the new cans in? For example...check any voltages, resistor values, bias etc? I have a very primitive grasp on reading schematics but I do have a DMM. Also thinkinung of picking up a Variac...they have a 500watt one for sale at my local electronics shop and I’m wondering if that would suffice:rolleyes:
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Yes, you should definitely check resistor values since the old carbon comp resistors tend to drift. The Sams has a resistance chart which makes it easier although you can also check individual resistors.

Voltages should also be checked after the caps and resistors are replaced. They will usually be somewhat higher than shown because wall voltage is higher now.

This uses cathode bias so there is no adjustment other than making sure the resistor value is correct and the voltage on the cathode is in spec.

You also want to make sure the coupling caps (C48, C58) are in spec and that they aren't (electrically) leaky. If they are leaky you'll see a significantly higher voltage on the output tube grids (pin 1-2) than is shown. Probably best to just replace them with film caps since they are lower quality ceramics.
 
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