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New Years Day - starting off with a Bogen DB-20


garyeanderson

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   I have the bad habit of doing a search for "tubes" on craigslist. New Years Day this DB-20 was listed at midnight for $50,

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there was a phone number ( I will rarely email, unless its just listed and I want it bad :rolleyes:) and I called. Made the appointment for 11am and brought it home.  Before I left I spied this old Altec 605B and commented that it looked pretty cool and as I handed the owner the $50 for the Bogen, he said "take it"

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The DB-20 had all of the tubes and the owner said he had last used it around 15 years ago and played bass through it, I kind of know what 15 years means so I opened it up to see what was inside

 

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It took a while to figure what was going on, the 8 mfd can cap that is just before the choke was bypassed so that just the choke and second 8 cap were all that were stabilizing the 441 VDC. It was made even harder to figure as all of the wires from the power transformer had grown a white layer of crud.

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I got a few Q-tips and the acetone out to clean off the wires, it was working but the Q-tips were falling apart so I found a small brush and continued. Once I could follow the colored wires I saw what looked to be two wires going from the same places so I unsoldered one to ohm them out. At this point I replaced the both 8 MFD caps with some new 10 MFD caps. 

 

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This picture is off the internet and is much, much cleaner

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I replaced the power cord as it was cracked and I didn't trust it. It wasn't long after before I powered it up. One of the 12AT7 tubes was dead so that was swapped out (all I could find was a 12AX7) and it was making noise again.

 

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now I need to figure out what to do with the Altec :unsure2:, the high frequency horn is open and the woofer is showing 50 ohms and if I push on the cone slightly it goes off the scale.

 

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1 hour ago, tube fanatic said:

Are you planning on doing a total restoration? All those caps shown in your under chassis picture must be replaced!  I would also look for out of spec resistors as well. 
 

 

Maynard

Hi Maynard

   I did not get it for High fidelity use, I don't plan on doing much more than I have done. It was used as a Bass amp and I plan on using it for a guitar amp (I know kind of sacrilegious, but I am a heathen).  Anyhow, I took the bottom back off after playing it for about an hour and did some probing with the volt meter and did not like what I was reading, what had been marginal was now over spec. The 441VDC was now 461 VDC so I reconfigured the first leg of the caps before the choke and installed a pair of serial 22uf caps with 2 - 270k ohm resisters between.

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This brought up the next problem. the voltage of the cap after the choke way now 451 VDC so I quit and went to bed. When I woke up, I went back to it and repeated the same thing after the choke.

 

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 and moved the 10uf cap that was on the plate to the screen.  The voltages had jumped up to 473 VDC off of pin 2 of the 5U4 rectifier and 461VDC on the plates of the 6L6's, the screens were around 363VDC, Cathode is at spec of 14 VDC and the grid is also on spec of Negative 10 VDC. I measures the 417h  VAC off of the transformer which seems a bit high seeing I was measuring 123 VAC at the wall vs. 117 which the amp was designed for.

 

some discussion of the DB-20 below

 https://el34world.com/Forum/index.php?topic=13511.0

https://el34world.com/Forum/index.php?PHPSESSID=gfcenspkbgsegp6k4uhl799ej6&action=dlattach;topic=13511.0;attach=29160

 

 

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1 hour ago, Randyh said:

Happy new year Gary , the Altec is too old to have an original cone replacement made from the original parts bin    - the  604 you have  can be as old as WW2 , the old cones  are unique ---------make sure the coil is good , as far as the tweeter side , replacements should be available from GPA -GREAT PLAINS AUDIO , they have the original tooling to remake the parts ,

 

- the altec looks really bad  --you have to check to see if the unit  needs to be remagnitized --------------------------------

 

-start by cleaning it -if the cone is bad ----------there are aftermarket kits --an original is the way to go , but it would be a newer part which is tougher than the old part , and made for the new 604-

remove the diaphrgam , very gently  -----------check  for corrosion , if you can find an average microscope or a very good  magnifier , you can check to see if the diaphragm is cracked- splintered ,-

Hi Randy

 

Not quite that old its a 605B so late 50's to mid 60's or so I have read. I am not sure what I will do with it, I have never re-coned a  speaker let lone one with a compression driver built into it. I have seen aftermarket kits for about $90 and "altec" ones for $130 and that just for the woofer, the high frequency I did not see. I am guessing it would cost 3 to 5 hundred to have it repaired and that is not in my budget. I got it because it "looked cool", the owner said it worked  the last time he used it (bass player). I will have to think about it for a while, it may just sit on the shelf as a conversation piece.

 

Gary

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Have started to buy a Bogen before for interest in the past.

Can understand the intrique,if

that is not too strong. Name has been around for some time with music, as you know. Many PA systems in the past for business as well... cool

 

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11 hours ago, seti said:

I got a DB20 just like the one you picked up wanna trade for the Altec lol.... I do have an extra DB20 anyway and I'll never use it.

 

They seem to weigh about the same, lots of iron like substances in both. UPS would love the trade, buy stock now...

10 hours ago, Randyh said:

- Gary   the aftermarket diaphragms go for peanuts and they are made of titanium  , Made in China -  this 605 would look , and sound good in your CW cab with a few adjustments ------

What I saw for $90 was a aftermarket paper cone for the woofer, the $130 was "altec" paper cone. I have an old Magnavox FM-13 table radio that would be just the thing to power the Cornwall clone with the 605B

https://www.radiomuseum.org/r/magnavox_fm13.html

 

10 hours ago, billybob said:

Have started to buy a Bogen before for interest in the past.

Can understand the intrique,if

that is not too strong. Name has been around for some time with music, as you know. Many PA systems in the past for business as well... cool

 

I think there are 6 Bogen PA amps in the collection,  the  H30 is pretty cool also - those brown t u r d s were swapped out for those orange drops.

Bogen was a great name and innovative to keep prices as low as the could to keep market share - just like klipsch did.

this Bogen H30 didn't work.jpg

 

 

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22 hours ago, seti said:

I'm in Little Rock if you decide you need a pair of the Bogen DB20.

 

 

 

Hi Seti

 

It may happen, I am not tired of looking at it yet, If/when I get some prices on re-storing the Altec then I should know more.

 

Back to the Bogen now, Sunday I cut the sides for the amp cover. I had a bit of Baltic birch left over from starting to build the Klipschorn side grills so I grabbed the two pieces. I thought there would be enough but only got three sides, the forth was a cutoff from some scavenged record player that I had my way with. There would have been enough but I changed the design and rabbited the bottom so it would fit over the amp. That meant I had to miter the corners so the rabbit would not show. I don't have corner clamps so I just glued them on the counter with wax paper under them and held them in place with a square to indicate I was close enough for a minute and left the house for an hour, when I returned - I repeated it twice more. By evening I had the open box below.

 

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When morning came I rummaged around looking for the top. Looked at some old drawer bottoms but they were I/4 inch lauan but I wanted something a bit thicker. Anyhow the guy I got the DB-20 from had a couple of speakers in the back of his truck that he was going to toss in the dumpster at work, one was a KLH model 5 so I grabbed that one and the other was a no name speaker that was made in Romania, I  figured I could get rid of it just as easy so that came home too. I had pulled the back and the veneer was lifting so I set it aside, the rest was a plastic veneer on particle board and I pulled the woofer and knocked down the cabinet and junked the rest. I save the back as it looked to be Baltic birch and you never know when you need a hunk to cut up. I thought it would work for the top and it had a hole for the speaker terminals that I could loose when I routed the opening for the air vent grill. I needed the template to route the air vent and looked around and I saw the pattern I used before (looks familiar? a Khorn side grill :smile:)

 

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   I cut it about 1/16 oversize and glued it in place, I added 3 more clamps after I took this picture. I gave a bit over an hour and sanded and routed the edges with an 1/8 inch round over bit. By 2 o'clock  it was ready for paint, just I was setting up the stuff to paint, the snow flurries started so I had to do something else. It had been 6 months since I changed the oil in the diesel pickup so I went and got an oil filter and a fuel filter, $58 and 30 cents - I could have bought another amp:biggrin2:. When I got back home the flurries had stopped so out came the paint and spray gun. 30 degrees is a bit cool for Rustolium 7777 so I sprayed the inside of the top and dragged inside to warm up, when it had tacked up out it went again to finish off the top

 

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Over night the paint dried and this morning I installed the perforated metal grill. Looks ok and fits even better...

 

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I may be done but I am sure I'll have the bottom of the amp off again, at least I'll have a nice stable base for it to rest on.

 

Gary

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