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New build: Mullard 5-10
New build: Mullard 5-10
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Old 17th September 2017, 10:44 PM   #11
alanpharwood is offline alanpharwood  United Kingdom
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jeromepiercy I'm using Electro Harmonix valves throughout and wondering if that is why I had a noise problem (with the EF86) and had to go to some lengths to fix it. You don't mention any noise problems so what valves you are using? As DF96 says it's probably the manufacturing variation - I'm using recently manufactured vs a Mullard product of the '50s but I have to say the DC voltages I measure are very close to spec. So long as they are relatively near it's no problem being as the valves are cathode-biased. Here's a pic of my finished amp. I'm getting 13W RMS into 16 ohms.
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Old 17th September 2017, 11:25 PM   #12
alanpharwood is offline alanpharwood  United Kingdom
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Default Transformers

Hi spiatrie, I've just been taking a look at your transformer question and I have the following observations:
Output transformer: looks ideal, has all the features I mentioned in an earlier post, so you can experiment with different loading configurations.
Mains transformer: a concern here. While the HT looks OK (80mA for normal loading is worst case) the LT side has problems (if I'm reading the spec correctly). The 5V 3.5A winding is superfluous since all the valves in the design use 6.3v heaters. This leaves you with two windings. Typically one winding is dedicated to the rectifier - if you use the EZ80 that's the 0.6A winding used leaving the 1.6A winding to supply the other four valves. The EL84s take 750 mA each, the EF86 needs 200mA and the ECC83 300mA so you don't have enough current! And you are restricted to low loading even though you have the other loading options with the output transformer. You need a minimum of 2A on the secondary to be safe. And 1A on the other to use the EZ81.
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Old 18th September 2017, 08:10 AM   #13
jeromepiercy is offline jeromepiercy  Europe
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alanpharwood I'm using valves all supplied by karltone.co.uk - 2 x matching pairs of EL84s, 2 x ECC83s, 2 x EF806s and one GZ34 instead of EZ81, as I built it stereo. A crackle noise and distortion problem did develop with one channel until the valves were warmed up. Swopping the EL84s cleared the crackle but moved the distortion to the other channel - so I suspect one of the EL84s is a bit faulty. However the distortion goes away after a few minutes. I may order another pair of EL84s. I'm planning to build the stereo pre amp and take the LT and HT from the main amp. I'm inclined to take up alanpharwoods suggestion of supplying the heaters for the EF86 in the main amp and the pre amp heaters with DC, as I suspect the hum will only increase otherwise. The gain on the main amp is huge - it's a no tone controls version - I'll save them for the pre-amp. Still sounds b***** marvelous hooked up to a bluetooth input!
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Old 18th September 2017, 08:11 AM   #14
jeromepiercy is offline jeromepiercy  Europe
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I must apologise to spiatre on my recommendation for the mains tranny, as I realise he's building/built a mono. So alanpharwood's calcs for the LT are far more appropriate. I should read posts more carefully next time.
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Old 18th September 2017, 10:03 PM   #15
alanpharwood is offline alanpharwood  United Kingdom
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Default Transformer

I think that mains transformer could have worked with the original statement where he said he was proposing using a GZ30 - which has a 5V heater and draws 2A. Then the other two windings would just be able to supply the 6.3 v requirement between them. But I was reacting to the later statement that talked about the EZ80.
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Old 18th September 2017, 10:53 PM   #16
alanpharwood is offline alanpharwood  United Kingdom
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Default Call me Al

jeromepiercy I noticed in your post no. 13 you mentioned interest in building the Mullard stereo preamp - I've thought about this too but I have concerns about noise especially given my recent experience with the EF86 - the preamp uses two per channel. The info in the Mullard spec gives hum and noise as 58db below 20W ("microgroove")which is very poor by today's standards. Coupled with the high sensitivity of the 5-10 it now does not seem a good match (to me). Would be a good topic to debate but maybe we should start a new thread - what does our friendly Moderator think?
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Old 19th September 2017, 05:43 PM   #17
musical noise is offline musical noise  Switzerland
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Quote:
Originally Posted by spiatrie View Post

I have studied my booklet more thoroughly and have discovered I should go with a low loading output stage because I intend to use the amp with music and voice only. For low loading the booklet recommends the use of a EZ80 rectifier.
From the Mullard datasheet linked below, pages C10 through C15 show distortion figures for the different loading conditions. For the low and high load conditions (6K & 8K pentode connection), THD is between 1 and 2% for most of the operating range. For the UL connections, THD is on average below 1% and in the case of the 8K and 43% tapping, it's below 0.5% with the D5 component not even shown (below instrument's capability). Since you're building new and have a choice for an OPT, I would take this info into consideration.

http://www.mif.pg.gda.pl/homepages/f...129/e/EL84.pdf
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Old 19th September 2017, 08:41 PM   #18
scottpetersen is offline scottpetersen  United States
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A possible reason for the variance in the DC voltage might be that one has the preamp connected, and the other does not.it is powered from the amp I think(from memory)
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Old 20th September 2017, 09:02 AM   #19
jeromepiercy is offline jeromepiercy  Europe
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Default Pre-amp for Mullard 5-10

Quote:
Originally Posted by alanpharwood View Post
Would be a good topic to debate but maybe we should start a new thread - what does our friendly Moderator think?
I'm up for it Al. I had a gut feeling that the 2 EF86's were going to be way too sensitive for the already sensitive 5-10. Guts are ok but science is better. I'm going to take a deeper look at the data and alternatives. Good screening and DC heaters would be a start. Then there's probably some good wheels out there already invented. This could be an interesting journey. My aim with a pre-amp is to use a magnetic pick-up for a turntable + some variety of other useful inputs + some tone controls. Suggest name for new thread - 'New build: Pre-amp for Mullard 5-10'. Rules say we can post new threads, but haven't figured out how to yet. I'm new to this game. Call me Jez ...
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