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Old 29th July 2007, 10:27 PM   #1
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Default SimpleSE and me

Upon completing the transfer of my monoblock tube amp from it's old beaten up chassis to it's new one I turned it on and it has a nasty ground hum. It also oscillates so I can't keep it on long to test and fix the problem. It does look good though, I wish I just left it in it's old case because it worked fine in there (besides shocking the crud out of me once (my fault))

My current system is a Crown Straight Line Two preamp and a Crown D60 original model amplifier hooked up to two medium efficiency Aiwa AFB-10 Flat Diaphragm 30 watt speakers. If any of you are familiar with these speakers let me know as I know nothing about them other than the internal chip amps sucked so I took them out and use the D60 instead. This setup works fairly well but I am still left looking for that "tube sound" that I lost when losing my tube amp. With school starting soon I will no longer have the man hours to fool with the other amp and so I was wondering if a SimpleSE board and two 6L6GC's would be enough to power the speakers I have . I will eventually get new speakers as money permits, but these are quite good the way they are now. (I have heard my boss' 4410A's with my old tube amp and they are to die for!)
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Old 29th July 2007, 11:37 PM   #2
kevinkr is offline kevinkr  United States
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Disconnect the feedback connection from the secondary, see if the oscillation goes away. Is this oscillation very low frequency? If so try swapping the plate connections to the output transformer, you may have them reversed.

The SimpleSE would be great project, and would probably work just fine with the speakers you have, particularly if you are not looking for obscene volume levels. (As these are probably not long term keepers I would go ahead with the amp and then look for a better match in speakers as time and money permit.)
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Old 29th July 2007, 11:46 PM   #3
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I am not familiar with your speakers, or the room size and your volume level preferences. The SimpleSE with 6L6GC's will make about 4 or 5 watts per channel in triode mode, and close to 10 in UL mode. You can run a tube amp quite a bit harder than a SS amp before the distortion sounds objectional, so I think that it would not be as loud as the Crown, but it won't be a huge difference.

Some speakers have terrible impedance VS frequency curves, and these are not ideal with any single ended tube amp that doesn't use a bunch of feedback (most of them).
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Old 30th July 2007, 12:00 AM   #4
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Thanks for the responses;

kevinkr : I have no ideal about the underlying circuit in this tube amp, I got it as a gift from a friend who knows I like tubes but never had the money (till now(new job! )) I don't know where the connection is but I will try reversing the output transformer connections. The oscillation is mid-high frequency that climbs in volume fairly quickly with time regardless of the volume pot setting. The hum increases very quickly in volume with the volume attenuator.

tubelab.com : my room size (bedroom) is 10x12 including the bay window. I listen at moderate levels, nothing really high and I like good sound over high volume. These speakers were fairly high quality when my parents got them in the 80s and were about $400 they sound very good and have good sound staging, just lacking in the lower frequencies. Also, I have sent you an email prior to this posting about the SimpleSE, it is about the same as my posting is here but could you give me a price on the SimpleSE with all component parts and the edcore transformers you used? I would really appreciate it. email was from -> aa@phloam.net
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Old 30th July 2007, 12:41 AM   #5
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Well I tried switching the the primary on the transformer and nothing happened, I think I found the feedback to the secondary and when I disconnected it the nasty hum went away but it still oscillates like mad.


EDIT: This is interesting! I played some music through it for about 3 seconds while oscillating and then pulled the plug with the music playing, as soon as the plug was out of the socket the oscillation stopped dead, also it is now variable with the volume control and does not "climb" like it used to, in fact the power transformer is making the same type hum I think. Maybe this is some type of heater issue? Again the "noise" is variable in loudness with the volume pot. Odd eh?
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Old 30th July 2007, 12:56 AM   #6
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Your email has not showed up yet. I will check again later.

At this time I am not selling the parts kit or transformers. I simply do not have the time or the financial resources to stock and kit all of the individual parts and transformers. I plan to add a small parts kit (all of the stuff needed to build the PC board) later on this year (after I get back from another trip in mid August). About half of my customers are overseas, and ordering small parts is often a hassle for them. Many have requested a parts kit. I am working to fit everything into a flat rate envelope for shipping.

Due to the high cost of shipping transformers, it just doesn't make sense for me to stock them. Edcor is in New Mexico, I am in Florida. If I have to get them shipped to me, and then pay for storage, I would need to add that cost to the transformer, and then add shipping to send it back out again. Shipping transformers overseas often costs as much as the transformer. There are many possible transformer choices also.
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Old 30th July 2007, 03:12 AM   #7
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Email Sent ! (again, but from different address)
I am looking forward to the parts kit, I think it will be a great addition for those of us that have trouble sourcing parts (me).
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Old 31st July 2007, 03:15 PM   #8
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you gety that email yet?
I really would like to order a board from you...and a parts kit
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Old 1st August 2007, 02:44 AM   #9
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I got your email and sent a reply. As I stated earlier, parts kits are not available yet. I must be out of town for a good part of August, and I will start on the parts kit when I return as time and financial resources become available. I will post the availability on the web site when they are ready.

I regret to tell you that I can't work on your amp. When I started Tubelab, I had to discontinue amp repairs and my consulting business. Between Tubelab and my full time engineering job, there is no time (or bench space) left for them. My listening room and lab is a 9 by 11 foot room with an L shaped workbench. A large project occupies 3/4 of the bench, and will until it is complete (October). The rest of the bench has either a TubelabSE or a SimpleSE on it. I must clear that area to work on anything else.

I have collected dozens of vintage amps myself over the past 10 years, thinking that I would eventually have time to work on them. I have realized that that isn't going to happen, so they will wind up on Ebay later this year.
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