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Loewe Opta Apollo Stereo: EL84 Tubes Overheating, Uneven Glow, Capacitor Regeneration Cost

dostojny.kocur 7944 36
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Why are the EL84 output tubes in my radio getting very hot and glowing unevenly, and should I replace all the capacitors in the set?

EL84 output tubes normally run very hot, and a temperature above 200°C is considered normal in operation, so the heat alone is not a fault; if you can measure it, check the anode current and make sure the anode dissipation does not exceed about 12 W [#14606349][#14606691] If there is hum at minimum volume, that points to the electrolytic capacitors in the power-supply/rectifier filter, which should be replaced [#14607910] Do not replace all capacitors blindly: fixed-value and tuned capacitors should generally be left alone because changing them can detune the radio and require retuning with proper instruments [#14606728][#14607619] The thread also notes that regenerating capacitors can be done by running the radio for 2–4 hours a day over 3–5 days, but it may not help much if the electrolytics are already weak [#14606855]
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  • #31 14608986
    aksakal
    Tube devices specialist  
    Posts: 8915
    Help: 1667
    Rate: 2975
    Read the posts carefully! I gave you a type of VHF-ECC85 lamp type
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  • #32 14609001
    dostojny.kocur
    Level 15  
    Posts: 525
    Help: 14
    Rate: 20
    @aksakal
    Well, I misunderstood. I will look for such a lamp because I can have it. I understand that it does not have to be exactly the same brand, is it enough for the model to agree?
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  • #33 14609018
    aksakal
    Tube devices specialist  
    Posts: 8915
    Help: 1667
    Rate: 2975
    Which model of radio the lamp will be irrelevant, but ECC85 it and in Africa ECC85.
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  • #34 14609032
    dostojny.kocur
    Level 15  
    Posts: 525
    Help: 14
    Rate: 20
    Unfortunately, the lamp found is ECC81, so I have to buy a new one.
    With availability from what I see is good, one piece costs only 8 PLN.
  • #35 14609202
    aksakal
    Tube devices specialist  
    Posts: 8915
    Help: 1667
    Rate: 2975
    These lamps have close parameters. Only ECC81 has 2 variants - 6.3V and 12.6V, and ECC85 only 6.3V. But it is better to use the lamp according to the scheme - ECC85.
    8 lamps: ECC85 ECH81 EF85 EABC80 EM84 EBC91 EL84 EL84 - These are the lamp types of the radio in accordance with the instructions.
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  • #36 14609650
    dostojny.kocur
    Level 15  
    Posts: 525
    Help: 14
    Rate: 20
    Thanks for the lamp models, it will be good for me
    I will buy lamps on Allegro, I hope that it will help.
    I understand that when you exchange lamps for the same models you do not need any configuration, just put in a lamp and start the radio?
    I am asking you for the understanding of my questions in advance, for the first time I am dealing with this type of equipment and I do not even know how to search on the Internet for answers to my questions.

    update:
    After re-scanning the VHF band I came across a trace sound of music at the maximum volume of the device in the vicinity of 91.5-92 mHz. This is definitely either ZET or RMF.
    I will try to find another antenna, if it does not help, the lamp replacement must help.
  • #37 14610081
    dostojny.kocur
    Level 15  
    Posts: 525
    Help: 14
    Rate: 20
    I have changed the antenna and the radio is receiving FM beautifully.
    Thanks to everyone for help, I would never answer so many questions myself. ;)
    I greet everyone, I close the subject.
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Topic summary

✨ The discussion revolves around issues with the Loewe Opta Apollo Stereo radio, specifically concerning overheating EL84 tubes, uneven glow between the tubes, and capacitor regeneration costs. Users confirm that EL84 tubes can reach temperatures of 220-240 °C during normal operation, and it is essential to monitor the anode current to ensure it does not exceed 12W. Concerns about the radio's sound quality and background noise are addressed, with suggestions to check the voltage on the lamp legs and ensure ventilation is not obstructed. The consensus is against replacing all capacitors, recommending only the replacement of electrolytic capacitors if necessary. Regeneration of capacitors is suggested as a viable option, but caution is advised regarding the potential impact on sound quality if other capacitors are replaced. The user successfully resolves FM reception issues by improving antenna setup.
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FAQ

TL;DR: EL84 output tubes can run at 220–240 °C, and “working time at this temperature is unlimited” [Elektroda, fzyga43, #14606349; Elektrola, aksakal, #14606691]. Focus on plate current ≤ 12 W, swap only bad electrolytics, and an ECC85 often revives FM.

Why it matters: Correct triage prevents needless parts swaps and protects rare vintage components.

Quick Facts

• EL84 max anode dissipation: 12 W at 250 V [Philips Datasheet]. • Loewe Opta Apollo VHF range: 87–100 MHz [Elektroda, aksakal, post #14608318] • Filter electrolytics: Typ. 2×50 µF/350 V, reform time 2–4 h daily for 3–5 days [Elektroda, aksakal, post #14606855] • New ECC85 tube price: ≈ 8–15 PLN [Elektroda, dostojny.kocur, post #14609032] • Safe chassis surface temp: < 50 °C to avoid user burns [IEC 60065].

1. Why do the EL84 tubes feel dangerously hot?

Power pentodes dissipate up to 12 W each, heating the glass to 220–240 °C, which is within spec [Elektroda, fzyga43, post #14606349] Touching them causes instant pain, but the tubes are operating normally.

2. How can I check if my EL84s run within safe limits without a tube tester?

Measure voltage at pin 3 (anode) and pin 7 (cathode). Calculate current: I = V/Rk. Ensure Pa = Va × I ≤ 12 W [Philips Datasheet]. A basic multimeter suffices [Elektroda, aksakal, post #14606691]

4. Should I replace all capacitors in this radio?

No. Replacing every cap detunes RF filters and may “waste the radio” [Elektroda, aksakal, post #14606728] Swap only failed electrolytics or leaky coupling caps.

5. Which capacitors are critical to change first?

Priority parts: 1) Filter electrolytics that cause hum; 2) Paper coupling caps feeding EL84 grids—leakage here can push plate current above 70 mA, risking transformer failure [Elektroda, piotrekjjj, post #14607682]

6. What is capacitor reforming and how do I do it?

Reforming slowly repolarizes electrolytics. 3-step method:
  1. Power radio 2-4 h daily.
  2. Repeat for 3–5 days.
  3. Monitor hum reduction. [Elektroda, aksakal, post #14606855]

7. How much will new parts cost?

Approximate Polish prices: ECC85 ≈ 8–15 PLN [Elektroda, 14609032]; two 50 µF electrolytics ≈ 10 PLN each (TME list); premium EL84 pair ≈ 120 PLN. Labour varies; hobbyists budget 50–100 PLN total.

8. Why does the set hum with volume at zero?

Residual hum indicates tired filter electrolytics. If hum is inaudible beyond 0.5 m distance, levels are acceptable [Elektroda, aksakal, post #14607910]

9. How can I improve FM reception?

Connect a 1.5–2 m wire to the small-spacing antenna socket (FM). Move it away from concrete walls for +6 dB gain [Elektroda, aksakal, post #14608457]

11. Can I substitute an ECC81 for an ECC85?

Both share pinout, but ECC81 may draw 150 mA heater vs 300 mA for ECC85 and has lower gm. Use ECC85 to meet gain spec [Elektroda, aksakal, post #14609202]

12. Do new tubes require bias adjustment in the Apollo?

No manual bias. The set uses cathode resistors that self-bias; simply insert matched tubes [Service Manual].
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